No particularly reason I can think of, guess it is just "one of those things" but it is interesting to note that the 2011 (US2012) GT-R rear diff fill procedure called for topping the diff up as normal and then using a syringe to draw 200cc of oil back out!
i did, went into safe mode when the main power module got a low voltage signal. that has been resolved.
well i didnt get to look at nor talk to the GT-R tech. This is all word of mouth from the service advisor. they topped it off and wrote off a Qt. of fluid but i dont know exactly how much went into it. I first noticed it after a 200 mile trip. Stopped for gas and noticed a burning smell, as if something got on the exhaust. got home and looked under the car and saw something burnt on the back of the midpipe. I'm going to inspect it further tomorrow. looks like the $7 seal is readily available, as for the flange it's on back order from japan. I'd sure love it if it was just overfill seeping out from the vent tube. it's been sitting in the garage for a few days and not a drop.
Rear diff leakage on the GT-R is quite difficult to detect visually. Both Pi-man and I have had them related to plumbing outside the diff, and detecting it is very hard. The pan under the diff can hold A LOT of fluid before any seeps anywhere. You have to pull the underpan to tell if there is leakage.
when you say pan, you talking about the carbon fiber under panel that covers the diff? that was removed and car was on a lift. used lights, mirrors, etc and saw what looks like a weep hole only on the left side of the diff. the fluid leaks out the seal, past the flange and down the little tube that is casted into the housing and then drips onto the carbon fiber panel. it still gets on the exhaust and runs down the panel. I didnt think i had a leak either - never had a drop on the garage floor, but the found the burn spots on the exhaust..
The problem is if you think you've "fixed" the leak, or are looking for another leak. It can "hide" by dripping onto the carbon fiber under panel, as you detailed. It then "blows" (because there is DESIGNED flow in that compartment to cool the differential and exhaust) onto other components (like your exhaust) Mine was often detectable ONLY by a small drip on the jack point ball, that didn't drop on the garage floor, just only when I had driven it out (and it was a couple of drips each time). So, I understand what you're saying.
