If its been diagnosed as nothing wrong and nothing is wrong, drive it. If there is something wrong take it back. You are undoubtably dealing with the reason it was sold. The other option is to sell it. Problems like yours are nearly imposible to repair if they go away.

You either need to leave it with someone dedicated enough to pursue it, give them the time, and then pay for their costs or you need to sell it.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician