Tiptronic ATF contaminated with diff gear oil?

[Dale_K]

Posted this on another site with no response so I'll ask here. My car (2000 S) showed a P0740 code, which I understand is related to torque converter clutch actuation. A local mechanic told me this could be caused by diff gear oil contaminating the ATF. Kind of make sense at least as far as the symptoms. I looked at the factory service manual and the contamination would normally seem to go in the other direction and the diff would become contaminated by the ATF, not the other way around. But a few pages later the manual said ATF contamination was possible if you pulled an axle without draining the diff first.

The question is has anybody seen a confirmed case of ATF contamination by gear lube? The mechanic said something about getting a lab analysis, which would be proof beyond doubt. I'm going to let him do a full Tip service and fluid replacement in any event. The mechanic said this kind of contamination was pretty common on high mileage Boxsters.

[Wayne 962]

Nope, I haven't seen it, nor have I heard of it until this post. However, the Tip has two separate functions (transmission and final drive differential), and there is a mainshaft that runs down the center that is connected to the pinon. I would imagine there is a seal that separates the differential fluid from the ATF. I would also imagine that the differential fluid would have a difficult time getting into the transmission fluid, as it's not pressurized - it's just sloshing around in the differential. I checked the parts diagrams, and I could not find any part number for that seal.

I would drain both fluids, and then see if you can visibly see any contamination between the two.

-Wayne