Re: Wich gear Oil ??And other oil questions!!
Not sure about 33's specificaly but a well respected Classic Car Specialist in the UK recommended using fully synthetic Oil in the Gearbox of my Giulia. His preferance was for Valvoline grade 15-50, or there abouts. He recknoned it made no sense to use heavy Gear Oil in the Gearboxes, because the Engine Grades give much better protection from cold. Be careful it doesn't run thro the seals tho, because it is much thinner, he also said fast changes when hot may be a bit noisy but from cold they will be better.
If you do a lot of short trips this is an advantage.
Swapping to semi synth, after full synth shouldn't make much differance IMO.