My memory is a bit fuzzy but i think i remember that about ten to fifteen years ago some automatic trans Diesel Ram owners were trying Mobil One Syn 5w-20 engine oil instead of ATF+2

I think the Diesel Trans forum in Canada had a number of posts on this

Perhaps some prior owner tried non synthetic 5w-20 engine oil in that 46/47 RH ?

Castrol Superclean is an impressive degreaser but one of the two formulations will attack aluminum if left on too long.

Grease Lightning detergent spray is also impressive on a few cruddy varnishes i have used it on, but be careful about breathing the vapor.