For what its worth, thought I would add my experience.
Firstly I had no idea what the PO had put in the gearbox, but it was baulking into second.
Tried the Castrol Syntrans, no significant change, then I tried ATF fantastic, very easy and quick to change
transformed the drive, but , found various online posts advising to only use as temp arrangement, plus it was
a little noisier on idle.
I emailed the well known LT 77 gearbox specialist, who do promote its use in their FAQ section, but i wanted to know if that
was still the case and they confirmed it was. But I found other refs to Motul Gear 300 as being the best by an expert on
the box, so tried that. Being honest I would say its just a little better than the Castrol and, by now I had, had enough of changing the oil, but when the box
is hot its a nice smooth change. its still a little stiff when cold into second, but i live on a hill so i usually change up within 20' of starting and into second
and then its warming up.