Recommended gear oil weight for 1964 Kiekhaefer 1000 Mercury Six lower end?

[e4g67]

I have a 1964 Kiekhaefer 1000 Mercury Six, 100 HP outboard motor that I am servicing (without a manual) and I have been unable to find information on recommended gear lube for the lower end. Does anyone have information on this subject? Thanks.

 

[Chinewalker]

Regular lower unit oil, 90 wt. Hypoid. If brand matters, use whatever your Mercury dealer carries. Keep in mind, Mercury was late to the stainless steel game and the shafts from that era are noted for pitting around the seal areas. Keep an eye on your oil color, noting whether it gets milky which indicates water intrusion.

 

[KristinTheBoater]

It would be recommended to use a synthetic blend 90 weight gear lube, but you do want to use what you have used in the past to prevent different weights from mixing. A good way to tell what was used previously is, by the color of the ear lube if it is a synthetic blend it should be green or blue ( a neon color) if it is premium 80 weight it would be more of an amber color.