AX-15 I use Mobil-1 10w30
I dont think 10w30 is anything like 75w gear oil
yes it is.
gl-5 is another story.
gear lube uses different numbers then motor oil for the same viscosties.
the gear lube for the ax-15 is a gl3 not gl5.
Can you explain why you use motor oil and not a 75w gear oil?