[T2] Trans oil leaking due to foam?

[MUTS]

I've dropped this engine thrice seeking an oil leak- first time, a year 
ago, I replaced the clutch and I think I did the seals.  There was a 
leak in 6 miles, it's been parked until I got to it 2 wks ago and 
dropped trans/engine combo.  The clutch was clean, the crank seal looked 
good, but throwout bearing had oil on it so I changed the trans-shaft 
seal.  Also made sure the weephole on top (behind nosecone) was clear.  
Transoil l I think I changed a year ago, it was clean and at the level 
of the fill hole.  Got it all in, RAN IT MINUS THE AXLES for 20-25 min 
to pump up lifters & it still leaked what was engine oil (could see it 
coming out along flywheel to trans seam).   Then wtf, trans oil was 
running down below nose/shift fork area.  Stopped the engine and cleaned 
the trans, ran it again, and no more leaking!  Dropped just the engine, 
changed the crank seal (and drove it all the way in with old seal); 
checked level of trans oil and it was below fill hole (had leaked a cup 
or more).  Got the engine in yesterday and ran it today again to pump up 
lifters (about 20 min- and yay, no engine oil leak.
But oil was leaking from trans- got flashlight, looked closely, it was 
running from above the nose cone (not from shift rod connection), 
dripped from middle of cone, and looked "foamy".  Again I stopped 
engine, got a mirror, cleaned it all up, ran engine and no more leak!  I 
pulled the fill plug and it felt low, but pulling out the finger showed 
the oil was all foamy.  Could this be overpressuring out of weep hole, 
and it still happens when low?  I just drained the oil, looked clean and 
nothing but one sliver on magnet.  What gives- can the spinning of the 
differential (remember, no axles) be an issue?  At local NAPA they only 
have 90 wt GL-4 gear oil and Gl-4-5 on the multiweight.  Can I use the 
90 when it never gets colder than 20 usually?  I understand that GL-5 
has too must of the additive that can corrode brass-bronze synchro rings.