[sjf911]

The leak-down can be normal with worn guides. The best way to check is to have someone follow you while you drive the car and see how much smoking occurs when you decelerate to a stop and then idle. Worn guides will typically smoke heavily (can be quite embarrassing) while stopped but clear under acceleration.

Unfortunately, I don't know of any accurate way to check for wear without disassembly of the heads. I suppose if the smoking is light and you don't have an indication that one cylinder is burning oil more than the rest then watchful waiting may be in order especially if mild driving is the norm. I have a low threshold myself but I have been the victim of a "dropped" valve before.