I read somewhere that the GX-77 was actually made by Fostex, except for the six heads, which were the last of the GX type made by Akai. Motors, gears, circuit boards, servomechanism are quite unlike anything in any other Akai R-R.
Over the years I believe I dismembered two Akai GX-77’s. However I never had this type of slow wind problem on those sets. It is likely that I might have a pair of ‘77 reel motors (somewhere) in a box, however, they are also 35-38 years old. It’s a LOT of work for me to locate them, so I guess it comes down to what you are willing to pay. Kinda pot luck.
I do have some torque scales, and might be able to apply 12v and a reel table, and try to get a reading, but again that sounds like hours and hours of work, with no reference for good, bad, or ugly on the results. Mostly this thread is about six years old, so perhaps it was already abandoned or resolved a few years back. Maybe put a photo of the problem part in this thread, as I also have other Akai R-R motors, and I know the GX-77 used different ones, but it has been decades… since I’ve seen the GX-77’s reel motors.
Steven