As for the longevity with a whining planetary, I had one that I ran for several years, and I later sold it that way. New owner blew up the slant some years later but the 904 was still happily whining. IIRC it was just Second. or maybe just First; I forget, I mean that was like 47 years ago. How do I remember the year? Cuz I bought that car just weeks before getting married, spring of 77; so help me I better not forget our anniversary. and the trans got my attention real quick.
I had taken that trans apart looking for the noise but couldn't identify it. Since it was just one gear, I didn't take it to the next level.
AFAIK there is only one ballbearing in a 904/727, which is used to steady the output shaft, out by the Speed-O area.
I also remember that the planetary whine is pretty distinctive.
I also discovered that when changing between the two gearsets, EVERYthing on the output shaft has to be swapped together. You cannot mix and match planetaries from an A904 onto an A998/999 output shaft. They are a matched set. ( EDIT; Actually, I think the change was at a particular year break).
I accidentally got this wrong, and within 30 miles the aluminum planetary had all the splines ripped right out of it. When I took the trans apart, I could not see a difference. Research revealed that to me.
Since I could not see the difference, I had to take another core trans apart, and this time swapped it all over as a set; problem solved.
