Re: TH400&NP208 Fluid Question
It is very common for the rear seal to leak on the automatic transmissions, and the fluid will leak into the adapter, and then into the transfer case. This is why GM switched to using ATF in the later NP205s behind automatics. Better to have all ATF than a mixture of ATF and gear oil. This will also overfill the transfer case, causing it to leak.
'70 CST Blazer, 350, SM465, NP205.
'87 Suburban 4X4, 350, 700R4
'01 GMC 2500HD, Duramax/Allison