Can anyone identify this gear oil leak on a C4?

[wkoperwhats]

When changing oil this weekend I noticed a big wet spot on the plastic transmission underpan on my 1989 C4 near the front (of car) end of the transmission. I pulled the front and rear covers to replace transmission/differential gear oil and investigate. After cleaning the area and replacing the gear oil, it became apparent that there was a drip coming from the driver side bolt that connects the transmission to the torque tube (?) leading to front differential. Just above this bolt is one of the hydraulic actuators for the AWD system, but the leak does not appear to be coming from that assembly. I've highlighted the drip in the photo below. It was *definitely* gear oil, there was no wetness on the passenger side bolt, and the both bolts were torqued correctly.



Ignoring the hastily repaired shift lever boot (not my work), can anyone give advice on what to look for to help determine the source of the leak?

Cheers.

-bill k

[LM964]

I know you may think different, but that bolt is below the longitudinal lock slave cylinder that on a C4 is prone to leaking with age. Had this same issue myself - the broken slave cylinder had allowed the the cylinder piston seals to bend and come away and allow fluid to leak into the trans housing then out down the end of the casing around the bolt. The rubber cap seal in the housing (that the slave cyl rod pushes against) prevents fluid entering the transmission itself.

A tell-tale sign should be the fluid level in the brake fluid reservoiur - is it below the max line and if you top it up does it drop again after a good drive or a good number of diff lock switch actuations (turning the console lock switch on/off many times)? Probably only way to be sure is to eliminate the salve cyl from your further investigation by removing it if you have good access and checking.

[wkoperwhats]

Nope, it's definitely gear oil. I completely flushed the hydraulics about a year ago and the brake fluid reservoir is still completely full. Overnight it leaked about 1/4qt. I'm guessing the rear main seal on the output shaft of the transmission. Does the tranny oil sit that high? If not it could be the shifter input shaft, but it doesn't seem to be coming from there. It looks like I will be pulling the drive shaft and torque tube off next weekend. I have the Porsche repair manual, and Adrian Streather's book, but does anyone have advice on where to find additional tips for that job?

Cheers.

[LM964]

Interesting. Aye, few guys have pulled these out for seal replacements @ rennlist. Check there.

[wgwollet]

Any update?