I've had the transfer case lubricant replaced as per Porsche's schedule, but no issues with the transfer case/gear sets themselves. I did just have to do my catalytic converters at 165,000 miles, and my oil level sensor had to be done at 160,000.
I did switch to an independent service facility that specializes in Porsches. They are very active in the Porsche rally car racing circuit, so they aren't just some guys claiming they know how to service German cars. They did the 160,000 mile service for 1/3 of what the dealer wanted, albeit without doing the transmission fluid service. Their take on the ATF service is, on high mileage vehicles with no evidence of transmission issues, its best to just leave them alone. Their experience is - you run the risk of draining the friction material that has worn off the clutch pads out with the fluid, and then you develop slipping with the new fluid. I posed the question to the service writer - what would you do if it was your car? He said don't do touch it.
I did also switch to BMW run flats with my new winter tires, and plan to do so for the summers when they need replacing. Tired of having to call a tow truck when I run over a nail and then having to wait a day or two for matching tires to arrive. Wish I had done it a long time ago. The car actually handles better with the stiffer sidewalls (265/50/19's).