In case you plan to tackle HVAC servo replacement, I found a link to instructions. Will benefit folks on here to have them.

Removing/Installing Servos - Cayenne 2003-2006 HVAC

There are more instruction on another main forum, with parts that are 100% compatible and cheaper (VW parts for Porsche - same company). Prices are half of what Porsche parts are. There are couple other threads on that forum discussing DIY steps, you will have to go there 'R'.

Good luck.