You had no wrongdoing regarding timing belt.

Timing belt breaking is unpredictable. You will not lose for timing belt issue if you did not claim that you already changed it to the guy.

Many states have so called "lemon law" which prevents saling defect car to others. Timing belt issue is not included when talking about lemon law.

Oil leaking is a common issue to a old used car.

if you dis not claim something related to the two issues, you will have good chance to win the case if he goes to court, depending which state you are now.