[blau911]

Never owned one, but have heard and read from reliable sources that the 996 Models are well known for their engine Rear Main Seal failure. Don't know what the exact failure rate is, but it requires either buying a new motor or tearing the one you have all the way down.
Even better, as a prospective buyer, it is hard to inspect to know if there is a problem, and there is no sure fix for it. In other words it could happen again