I don't have any knowledge about the Cayenne, but since it shares 90% of its parts with the VW Toureg and is constructed on the same line, that is not a good sign as the VW's have been plagued with numerous problems. We own a Passat W8, which has been far from a trouble free vehicle but everytime we are at the dealer, there are Toureg owners there complaining about some pretty serious problems.

You might also be aware the MDX is suffering from transmission failures. At the moment it seems to be affecting 01s and 02s, but the problem is bad enough there is a forum devoted exclusively to this problem.