Don't use graphite!! Automotive locks use a grease from factory to lube them, although by now it may be all gone but none the less if there is some remaining the graphite will bond with those grease and effectively bind the wafers up even more.
The cylinders are super easy to remove, (explained many a thousand times before) your best bet would be to remove the lock and run it down to a locksmith and have him replace the wafers and cut a new key from code. This will by far be the cheapest thing to do, because of the split wafers in the lock you chance making them become completely jammed when you apply the graphite and it will cost a considerable amount more to get it fixed.
Yes some have had success with the graphite in the past but have just been lucky, if you don't trust any locksmith in your neighborhood just call AAA and see who they use.
Good luck