Tom,
I'm no attorney, but here's what I would do if I wanted to proceed without the benefit of paid legal advice. I would send a registered letter to the seller's attorney (and an email telling him to look for the letter) offering to close the deal as previously agreed subject to the following stipulations:
- The car is in the condition described in the deal.
- A clear title document is provided at the time full payment for the car is provided.
- The deal is closed not later than (date you choose).
I would close by saying that I entered into the purchase agreement based on assurances the deal would be done by (date) and the car would be kept in very good condition until the sale was complete. But if those conditions are not met, I will consider the sellers actions to have voided the agreement.
Good luck.