[tbucketnut]

Good point Lewis, The 64 will get an R&R in the next couple months, its gear oil looked to be original when I changed it out last month. It was the nastiest I have seen too.

Some of the latest and greatest synthetics lubes I have found are so slick the synchros (especially worn used components) have a hard time meshing the gear as smoothly.

I believe mineral oil was oem until mp gear lube came along it was gl-1. When that happened must of been into the 60s some time.
I believe some sm420s found there way into many new vehicles after that into the 80s maybe abroad.

Thanks for your point.