Gear oil for trans and rearends

[Brock]

So my transmission finally crapped out and I went to a gear place to get my parts to rebuild mine, they also rebuild them and the guy I was talking too has been doing trannys for 40 years... the topic of gear lube came up.

He says for every guy who says he's had luck, 5 don't.

His opinion is that the gear lube would theoretically be better for the main case but it's the syncros in the aux section that have trouble getting properly lubricated with the thicker oil, specifically the inside shown in my pic....
   

Especially if it's driven by a guy who likes to flip the range selector in nuteral.