Yep, the presence of the friction modifier won't hurt a thing in an axle without the LSD. The reusable gasket is called a Lube Locker which can easily be found for sale all over the internet.
I agree with the advice to use dino (conventional) gear lube for the reasons Currie requires its use to keep their axle warranty in effect... axles run cooler with a conventional gear lube than they do with a synthetic gear lube. That was surprising news to the people who conducted the tests that confirmed that.
If you tow or wheel in hot weather, stick with a higher viscosity like 80W-120, 90W-140, etc. If you don't tow, a 70W-80, 75W-90 is fine.
Torco 85W-140 is excellent stuff for pretty much any type of use, Currie resells it with Currie's name on the bottle.