Losing transmission fluid, milky fluid coming out

I have a pcm 87 351w with a 1:1 BW tranny. At the end of last season after installing a new (used) Windsor and tranny, upon my first startup as I ran it, I noticed a pink milkshake coming out from where the engine meets the bellhousing. I checked the tranny fluid and it was full of water and tranny fluid. I had my parts motor that I pulled my known good tranny cooler from, suspecting a bad cooler. I put it in, flushed it 3 times, ran it and it appeared all was good and I laid it up. I re-commissioned it today and while running I started checking the tranny fluid and it was barely on the dipstick. At that moment I looked and saw it was leaking a pink milkshake into the bilge again, however the fluid in the tranny is still clean just seeping out a milkshake on the front of the bellhousing. I have been reading other posts and I'm not sure which seal is bad? I would appreciate any advice anyone can give. I'm on motor two in just under a year and would love to be able to fix this without pulling the entire motor for the third, fourth ( I've lost count time ). I've read of just using bottle jacks under my manifolds and separating the two but from there I don't know what's next?

Pete, I did not do a rebuild on the tranny, last fall when I installed everything I started her up found the leakage AND had it in the tranny. Yesterday, after getting it to temp it started to seep again, from there I was literally putting fluid in as it was running and it was just seeping right back out, however what was actually in the tranny was clean, just leaking out just rear of the oil pan. I do have my other tranny that worked perfect in my barn setting? Would I be better to just swap?

Gotcha, ok anybody interested in the tranny that needs rebuilt?

Update: I pulled the tranny, bellhousing and damper plate, I got a hold of a reputable shop to do the tranny swap and align everything after for around $300. It seemed like a good price to pay so I didn't make a mistake trying to do something I know zero about.