There was/is a misconception sometimes that GL5 gear oil attacks the brass/bronze syncro's in the tranny's and causes them to fail, I remember reading all this hoopla on JU a long time ago, anyway, people were running ATF, GL2, etc.
After checking with a petroleum engineer, older GL-5 had an issue with "some" metals, but that's all been cured for many years.
GL2 doesn't have that issue, but it doesn't have the anti-foam properties (it's a low speed, high load lubricant)
GL5 all the way, and maybe some Moly additive, but that's about it.
My 2 cents
