I would rather keep oil in it. There are two things.
I see many have commented on the vent. IF the Vent is clogged.. Well See above. We will leave that to their knowledge as I personally have never seen that happen. but then I ... My Experience is very very limted (ONE RV, the One I'm sitting in, on this issue)
IF the seal is actually bad.. NOT the axle seal but a power steering seal.. Not an RV but a Car, and not mine but my MOTHERS.
Every time she did a hard left turn (As I reecall) the seal blew. EVERY TIME.. IT was replaced under warranty several times till the warranty ran out and the dealer changed hands. he replaced it (at his own expense) one more time but was not all that happy with the service record so he sent his steering guy to Hamtrammack to study at the factory..
Came back and found the shaft it sealed had a "Burr" (Rough spot) that was tearing up the seals.
It can happen on an axle too.
