I have a 1993 GMC Sierra Z71. It's been leaking transmission fluid for a month despite the 3 front seals we put in it. We are now starting to think that it is leaking from the oil pump gasket. We want to take the transfer case off between the trans and what seems to be a transfer case adapter. My only concern is if there's some kind of o-ring or seal that would need to be replaced because I can't find any. The only thing I can find is the gasket between the adapter and the transfer case. What would cause this thing (4L60E) to leak so bad, and what's between that adapter and transmission?