Oil foaming inside gearbox?

[STINGER477]

Just finished rebuilding my K-Way gearbox,(new bearings and seals). I also installed a sight glass so that one quart of gear oil can be seen at the half-way mark in the glass. I put the box back on the boat an test ran with no prop for couple a minutes up to about 3000 engine rpm and noticed that the oil in the sight glass seemed to be foaming. I did change oil brands, it had rotator oil in it and I changed to Lucas 85-140. Anybody know if this is normal? I had heard that when you get a foaming gear oil that it causes premature wear on the seals.

[Dirty1]

automotive gear oils are designed to foam, thats how the oil gets down the tubes to the wheel bearings. you need to find a gear case oil from like mercruiser or volvo penta.