If you look at the note at the bottom of the picture it says, "What NOT to use In your SM420". Ken uses it in his newer transmissions so I thought I'd try a synthetic when I rebuilt it last fall. The syncros didn't have enough grab with the synthetic oil and it would clash the gears going into forth every time. Switched back to the old standard 85w-140 Mystic and all is well now.
Denny G


Denny G
Sandwich, IL