I take your points. I based my opinion on quite a sizeable article in GoMog detailing the LT77 gearbox.
It explained that there is a small pump with a plastic impeller which is easily overwhelmed if the oil is too thick, with catastrophic consequences.
I am grateful for the information about Castrol Syntrans, which I am keen to install.

Incidentally, I replaced the diff oil today with MPM 75W-140 fully synthetic gear oil at £27 per litre.
Owners manual said 1 litre, GoMog said 1.3.
Actually probably 1.4.
Now if only the gearbox access hole was on the same side as the filler plug.

Last edited by Phil+8; 26/09/20 03:37 PM.