I try to use different oil in all holes ... Mobile 1 in the engine, Redline Shockproof in the transmission and either Redline Primary oil or ATF in the primary. Because each is colored differently you can easily see which component is leaking.

Now if you have a leak in the primary area, it could be from a warped primary cover, meaning that it was removed and not torqued correctly. Or possibly the oil seal in the inner primary cover (which seals the transmission main shaft) is leaking.

Twin cam engines don't really leak all that often, at least from my observation. The transmission seals are fairly solid also. Seems like the primary is the usual suspect.

Hey but what do I know ....

 

I bet you $5 that the leak is coming from the derby cover, particulary one of the bolts. The warm oil will drip off of the primary and barely leave a streak so it is hard to notice. I had the same problem on my RK and that primary plug was the suspect for far too long.

The fix was to use the derby cover gasket with the RTV on it, and ad a thin layer of RTV on top of it. That solution has workd great. A slightly warped derby cover from overtorqing or something can be hard to detect but that oil will find a way through.

How to prove this: The talcom powder guy was on to something. Better idea is to get a can of spray deordorant that leaves a white film. Wipe everything down and spray on all over the primary and under suspected areas. The suspect will leave a trail to the scene of the crime. make sure it is clean first.

You could use RTV on the drain plug if that turns out to be the problem, but you have to clean the threads very well. I use the orange stuff because of the very high temp rating.

GL. leaks suck.

 

Check the tranny vent. If you overfilled the tranny even a bit, it will find its way out of the vent and drip appearing as though its coming from other places.