Contractor may have bumped a/c unit during work and resealed it at a tilt which is now causing it to leak.?

Your problem here is one of proof. You would need to have some proof that these people caused the damage and that it was through some negligence on their part. Even you don't seem 100% sure that they did it and that this isn't simply a matter of regular wear and tear springing up, so you can't very well except to prove the case in court by a preponderance of the evidence. It looks like you are going to get stuck with the cost of repair on this one.