Originally Posted by APIDavid

It is worth a go but the science is that the baulk rings force the oil film away from the gear taper that it sits upon. If the oil is thicker it will make it harder for the baulk ring to dissipate the oil. It may work on the basis that whilst squeezing the oil out of the way the baulk ring manages to slow the gear down better and then has an easy time of engaging.

BUT thick oil saps power and may be hard to engage gear at all on a cold morning.

Best to use top quality correct grade fully synth. BUT if the box is knackered the best oil in the world will make no difference.

David APi