A/N - I do not believe that when it came to changing the licence plate on the Impala, that Dean would ever have let Sam be responsible for it, as shown at the start of "What Is and What Should Never Be." Therefore, this is my take on what happened between leaving Green River and turning up in Illinois for the Djinn hunt.
"Move it Dean, we need to get going."
Sam' voice from the front of the car sliced through Dean's contemplation, he quickly stowed the item he had been holding, no caressing, into his duffle, did up the zip and flung it into the trunk, before slamming the lid.
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"We're out of rock salt Dean." Sam called to his brother.
Dean's head appeared over the rim of the grave he was digging, "Nah, there's some in my duffle."
No sooner were the words out of his mouth than he froze, realising what was going to happen next. Several seconds passed before Sam's voice rose in anger, "What the hell Dean?"
"Look, I can explain," Dean began, hauling himself up out of the grave, but Sam cut him dead.
"Forget it Dean. What's the point of changing if you are going to keep this?"
"She's always been with me dude, I just couldn't do it." Dean replied, a look of whistful nostalgia on his face.
"It's just a licence plate Dean, you still have the car."
"You never did understand, did you Sammy?" Dean replied, his voice barely above a whisper, his words meant for him and his girl only.
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"Y'know this is killing me right? I mean, it feels like I'm losing and arm or something." Dean groused into the phone.
"Suck it up. You can't keep the plates, every law enforcement agency in the country is gonna have it on their Hot Sheet. It's gonna be hard enough to convince 'em that two guys in a cherry '67 Impala, even with different plates, aren't the ones they are looking for."
Dean stifled a snigger at the innocent Star Wars reference, guaging from Bobby's tone that he wouldn't appreciate it.
"Okay, I'll go see this guy, uh, Sheehan." Dean capitulated, finally realising that he was going to have to go through with this.
"See ya Dean." Bobby said by way of a farewell and hung up before Dean got a chance to reply.
Dean slammed the payphone handset back into the cradle and stalked across the parking lot to his car. Sam was in the Circle K across the street buying what passed for dinner in the Winchester's world. It would take him a while so Dean decided it was time to say goodbye.
Sliding into the front seat he ran his hands over the wheel, feeling himself sink into the depression in the leather of the front bench that was the result of so many hours driving. He smiled at the way the leather formed around him, more tender and knowing than any lover's embrace. He inhaled, the familar scent of leather, both from the car and his jacket, mingling with the odour of stale potato chips from the open bag he knew was lodged somewhere under the front seat, and a vague waft of gun oil from the cleaning kit on the back seat.
Somewhere deep down, Dean knew he was being foolish, but a little further down, nearer the core of who he was, there was a part of him that saw his car as much more than a means of transport. It was a link to his dad, the most tangible one he had besides Sam, but it was also about the familiarity. It was the one thing that hadn't changed in his life, even when everything around him was being shuffled like a deck of cards, there was the car. The rock in the centre of the pool. Sure it would still be the same car when this Sheehan guy was done, but something wouldn't be off.
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Dean paced the room like an expectant father.
He and Sam had driven flat out for several days to reach this wreckers yard in Illinois from the Green River Correctional Facility. Sam had slept a lot as Dean had insisted on doing almost all of the driving. Taking the time to commune with his car, apologising silently for what was coming next.
The guy Bobby had sent him to, this Sheehan, was about as understanding as all the rest. He grunted when Dean introduced himself, stuck his hand out for the keys and then, once Dean had handed them over, pointed towards the sty that passed for his waiting room.
It was here that Dean was trying his hardest to wear a rut in the packed dirt floor.
"Dean, will you quit pacing, it's only been ten minutes, it's gonna take him a few." Sam snapped, but Dean wasn't listening. He had seen the glint of early morning sunlight on polished chrome and ran out to see what had been done.
Gone was the licence plate he'd always known, the first thing he had really learnt to read so that he could find Dad if they got separated someplace. In its place was something that felt like a cheap knock off, like a Metallica track being covered by a boyband. Dean suddenly felt like he imagined a small kid would when his mom came home from the salon with a new hair style, yeah it was still mom, but not quite the same one you knew and loved.
Ohio plates, legit looking licence tags, and no damage to the surrounding bodywork. At least Sheehan was efficient.
Sheehan was beside Dean handing back the keys, "Dey're untraycable, but legal. Oi tossed the auld ones in de yard. No-one'll foind 'em." The little man's Irish brogue was certainly undiminished by his years in the US, but Dean got the gist and nodded, taking the keys.
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Dean suggested to Sam that they find a motel and catch up on some decent sleep. During their time at Green River neither brother had slept that well, coupled with their cross country trek of the last few days they could both use it he insisted. Sam acquiesced without a fight and Dean drove them to the nearest motel in quiet contemplation.
Dean awoke with a start and was shocked to see it was now dark. He hadn't intended to actually fall asleep, but now he realised he felt more alert, and that the cover of darkness would help with what he had planned. As soon as he was sure that Sam was still soundly asleep Dean rolled off the bed and headed for the door. He had fallen on to the bed still fully dressed to ensure that he wouldn't wake Sam when he left.
Outside the motel, the Impala was parked on a slight slope, Dean got in, let off the handbrake and rolled a little way down the hill before keying the engine. He had planned it all on the drive to the motel, all except for the sleeping part, but that was working to his advantage.
Dean drove the few short miles back to Sheehan's yard, killed the lights and engine and coasted to a halt near the back gate.
A minute later he was among the rusting hulks of Sheehan's previous victims. Without a clue where to look he cast his gaze wildly about until it lit on the object it was searching for. He lifted it reverentially from the muddy puddle it was resting in, slunk back out through the open gate which he was careful to re-lock, before dropping his treasure into the waiting maw of his open duffle bag.