I was wondering what the effect of a small rear main leak would have on a 4 speed setup? I do not have a 4 speed but was thinking about swapping over to one. I presume it would be bad. Any 4 speed guys out there with the small rear main leak?

If you're thinking about the possibility of oil-soaking a clutch its not likely. I had a small rear main leak and after tearing into it the clutch was in no danger

But that said--why not fix the rear main? I did.

I had a small leak that I let go for months which got fluid on the trans and exhaust. While no major problems, the p-i-t-a was having to clean the underside especially cooked oil on exhaust. I am glad I took the time to fix it. Go the extra distance when swapping in your new tranny.