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So I took it apart again. I did as you said and found the breather with a mirror. It was dirty, but dry. There was no fluid up there. I took a paper towel and wiped it clean, then thumped it a couple times with my finger to make sure it could move freely. I also filled it to exact capacity after letting it drain for about 45 minutes. I measured 2.9L and filled it up. I think gave it one more pump from the fluid, which caused it to start leaking out the fill plug. I let it sit for ~30 minutes until it completely stopped, and closed it up. The leak is still there. At this point I think I'm going to have to bring it in. I don't have the tools or space to do much more than I have. I would prefer to do it myself to save the money, but I have 30 hours into this thing already and I'm still at a loss for what the problem may be. If it's anything more serious than the seal I'm not able to do it at home.
Do you think it's actually likely that oil would be coming from there? My biggest concern is that maybe the seal isn't seated properly. I bought both seals listed in the PET diagram -- there's a 70mm and a 68.2mm. It's not clear from the diagram which was supposed to be used. Looking online the 68.2 is the "right" seal which would be passenger side on the car, but since the transmission is in "backwards" it would actually be the driver's side. When I pulled the old seal I took both new ones and compared them to make sure I was using the one that matched. The 68.2mm was the same size as what I pulled, so that's what I used. I read a DIY here or on another forum and the person who did it (same side, driver's on the same year/model) used the 68.2mm as well. The 70mm clearly does not fit (I did try it after the first time I replaced it and it continued leaking). The 68.2 fit without much trouble. There's friction but it didn't want to deform like the larger seal. As with the DIY I read, I made a seal driver from 2" PVC coupling with an end cap. I shaved it down a bit on the drive end and used a combination hammer and mallet to knock the seal in. There's not much room to get a good swing, but I believe I got it.Shining a light in there, there's a slight gap but you can see the edge of the metal plate it is seated against. The seal appears to be seated completely on it with the gap showing because that plate is not actually circular on its inner "hole" (it's clear when you pull the halfshaft, kind of hard to explain but it's more elliptical than circular). I'm going to drain and refill it again and see what happens. I'm pretty sure it's still overfull, and I have replaced seals like this before (just not on this particular car). I'm reasonably confident I didn't screw it up I'm just baffled. The reason I asked about too much fluid is that I read in another article here or somewhere that someone finally found their transmission leak (they had a shop tell them to replace the axle seal and it still kept leaking) and it turned out there was far too much fluid in it.
I have a 2006 997.1. Recently I noticed that the plastic cover at the rear of the car was covered in oil. After pulling it it was obvious that it was gear oil from the transmission, and that it appeared to have come from the left (driver's) side axle. I pulled the halfshaft and replaced the seal. I then refilled the transmission and the leak has not gone away. I figured I screwed up on the seal, and replaced it a second time just to make sure I hadn't lost the tension spring or whatever but that didn't do anything. My next thought is that it was probably overfilled. The book states 2.9l, but my assumption is that it can't actually take that much during a change -- only when filled from dry. After some googling I found some references to 2.6l when doing a change, though I've not been able to verify that in the owner's manual, service book, or anywhere else. I started slowly draining fluid and driving around the block to see what happens. As I drain more fluid it leaks less and less. However, I don't want to end up with too little so I'm not sure what to do here. The seal was an easy change, but I'm not too keen on doing it again because I'm pretty sure that's not the problem at this point. Does anyone know if the transmissions on these cars might have some kind of vent on the driver's side? The passenger side is dry and clean and there haven't been any problems with it. Is it likely that it's still overfull and the seal is really meant to prevent excess from splashing out and too much oil will still find its way out? From what I see those seals really can't do much to hold anything in if there's an excess of oil being thrown at it.