Help chasing Oil in Bilge

[windsurfnut]

I have an oil leak somewhere, it keeps showing up in the Bilge water,even after cleaning the bilge well. It looks like motor oil, light brown. However... My oil level does not change at all, but my transmission fluid does disappear during the season. What stumps me, is that the transmission is red, and there is no red oil in the bilge. I guess it's possible the leaking transmission oil is dirty and becomes brown, but on the dipstick its still fresh red looking.
I cannot find a leak anywhere, and we get enough bilge water using the boat that its never dry and traceable. Originally I thought Rear Main Seal, but again, no real source of a leak to be seen under the bellhousing. Quick drain fitting?
Any guidance?

Forgot to add, 2002 Ski Nautique with GT40

[SilentSeven]

On my prior boat - 1997 Ski GT-40 - my leak was the front transmission seal. Apparently this is quite common and you can check by feeling for lubricant at the base of the bell housing. $10 part.

I replaced by myself...all in all it was pretty easy given the location of the new part. Removed the exhaust hoses between the manifold and the muffler. Disconnected the drive shaft, all the linkage bits and undid the rear engine mounts. Loosened the front engine mounts so the motor would tip. Tipped the engine forward and put a block under the oil pan. Removed the bell housing bolts and slid the gearbox aft. It wasn't that heavy (70 lbs?) so I was able to pull by hand. Replaced the seal with a part from Ski-dim and re-assembled and did a shaft alignment. Probably a 6 hour job if there are no problems and it's your first time. Likely can be done much faster after you've done a few.

Cleaned up my bilge nicely. This was on a 1500 hour engine.

Edit: BTW, the tranny oil looked brown, not red, in the bilge.....

[windsurfnut]

thanks SilentSeven. I did the rear main seal and damper plate in my 1988 MC Prostar with the 351, so familiar with the process. Not that I really want to dig in that far again.. hope that its just the transmission seal, and given the loss in transmission oil, and that it can be brown in the bilge, I'm feeling better about changing that seal and not the Rear Main Seal.

[SilentSeven]

Right. I was also confused by the brown color at first.

Obviously you can get a good look at the rear main once it's apart and - like you - I was nervous as to what I would find. My rear main was all good and the leak was clearly from the front tranny seal. Given that you're loosing some tranny fluid and not engine oil, seems like the tranny seal is a pretty safe bet.

[windsurfnut]

thanks again SilentSeven for the confidence in the search. Bellhousing has red oil on it. Time for a new front seal

[windsurfnut]

know the part number for the front seal by chance?

[windsurfnut]

Am I right with R047185? And might as well grab a R047187, as its cheap and I'm right there if I need it?

[SilentSeven]

I'd call Ski-Dim; they'll know right away. I do seem to recall they also recommended replacing a transmission o-ring that's easily accessible when you pull the front seal plate. It was a real simple add on.

One more thought - get a shaft protector or a backup seal. When I re-mounted the front plate, I thought I might have nicked the seal on the input shaft. As I wasn't 100% sure and didn't want to do the job a second time, I got another seal and replaced the suspect one. On the second install, I carefully wrapped the spline shaft with painters tape and was uber careful to not let the seal bang on the spline shaft.

Found a few pics...sadly didn't take too many.

- grimy bilge before job - https://1drv.ms/u/s!AoJnMC1oR2hM7KQL6ZACc9bHDjFBwA (btw, in the top left...thats mold, not grease!)
- front of trans with seal plate removed - https://1drv.ms/u/s!AoJnMC1oR2hM7KQPVQbnfrZMcJ4RrQ
- seal plate with o-ring mentioned above - https://1drv.ms/u/s!AoJnMC1oR2hM7KQQVx2NQWQBGSEmWg