I know there are hundreds of threads on the manual transmissions and what fluids to use.
I ran across this site Lubricant for New Venture Gear 3500, 4500, and 5600 Transmissions
and was considering the Mobil 1 synthetic 5W/30 for my NV3550.
A few months back I changed the oil in transmission to Pennzoil Synchromesh (used jeep with 100,000 miles). It did quiet the marble rattle noise that I've read is common when in neutral, but lately with the colder weather it is not shifting very well. (The pennzoil synchromesh is not synthetic)
I've read all the details and have seen that in the AX transmissions a 10W/30 motor oil has been recommended so motor oil must be low sulfur and not damage "yellow metals".
The reasoning in the article seems to agree with other sources I've found on the NV transmissions.
Has anybody run a synthetic motor oil in their NV3550 for extended length of time? (or even in the AX series of man. transmission)