I've always run a cup or so of Slick 50 ATF additive in my M46 for the past ten years. Never had any problems w/ the OD operation or shifting. It's a little viscous so you need to dilute it a bit with ATF to pump it in. I just use an old trigger oil pump with the spout removed.

OD shuddering and occasional dropout have been happening to my 83, too. No fluid leaks, but the problem is definitely heat-related. After a good run on a warm day, the OD shudders if you get below about 45MPH. This does not happen earlier in the drive, or on cold days when things are not yet fully warmed up, and therefore the fluid has not thinned out. Low fluid level will also make it run hotter - so, same issue.

The base cause, as explained by "OD Guru" Duane Hoberg, is worn piston seals failing to hold engagement pressure when the fluid gets hot (and thin). I bought his kit of seals and improved pistons - not installed yet, tho.

Duane is not a fan of Redline's MTL (manual trans lubricant), but examining its specs I noted it holds its viscosity at higher temps better than ATF, and has a higher gear-wear rating. I noted smoother shifts and better OD performance when I changed to it on both our 240's. It's expensive, so find and repair those leaks first. MTL is not the final fix, but a good bandaid.

If you topped up the trans with the car's front end elevated, it would take more, even if showing full while level. I've done this to deliberately overfill it a little.


--
Bob (son's 81-244GL B21F-M46, dtr's 94-940 B230FD, my 83-244DL B23F-M46, 89-745(LT1 V8), 98-S90, 77MGB and four old motorcycles)

Its possible that as you drove the heat within the tranny built causeing pressure etc you see where im going, its also possilbe that it had to do with the driving conditions themself! i just helped a buddy drop his out and resealed the top of the tranny, the entire seal blew out big job

Whether or not you got ripped off is hard to say. Even if you did, how would you prove it?
--
FCP Groton