To second Ed on getting the annual now from a dis-interested mechanic...If you find something now, you may have some bargaining power, or else, it's a good time to move on to the next one down the road.
If you wait for 6 months for the annual, and then you find something wrong, you'll have the devil of a time trying to prove that the fault existed at the time of purchase. Even then, you'd have no recourse with the seller.
There are no real guidlines on a prebuy, just whatever the buyer and his mechanic decide on. If you say you want an annual inspection, that scope, at least the minimum to be FAR compliant, is defined in FAR part 43. Then, you'll be off to a fresh start and if you assist, or at least look over the mechanic's shoulders (without getting in the way), you'll have a good understanding of at least what goes where and what looks okay, and what doesn't.
My suggestion...do not be afraid to ask all the questions you want to with your mechanic. If you're genuinely interested, a good mechanic will be happy to have you as a customer. If you nit-pick the mechanic and second guess everything he does, well.... he may not be able to make time for you when you need him next... That passive-aggressive behavior...
Congratulations on the find, and you're the perfect example of using this group to it's fullest when looking for a plane. Not to mention, you titled this thread perfectly!
Good luck with the prebuy and the title search. As for the stall horn not working, that's an easy fix. Inexpensive, too. If that's all there is, you should be all smiles.
