Best lower unit gear oil for a very old motor.

Any special considerations regarding LU gear oil for a 64 year old motor?

Thanks Pappy. Just wanted to make sure modern lubricants won't adversely effect any internal components of a motor this old.

Yes any modern outboard gear oil will work great... much better than that old crap in the tube used to... You don't need to worry about that on older motors.....

When I turn the motor over manually by the flywheel with the motor in gear, the prop turns with no weird noises. However, then I pulled the upper and lower drain plugs on the lower unit today, absolutely nothing came out. Not really surprised, but I am concerned. Should I flush out the housing with something first to look for metal shavings/Chips or just refill it to find the leak? If it should be flushed first, should I just use the lubricant or something else. Little concerned about possible sludge buildup to.

Thanks for the info, Pappy. It's a 1956 Johnson 10 horse, model QD 17 B.

Are you sure the previous owner didn't drain it ? I always want to look things over before I bet a fishing trip on it... but you might still be perfectly ok.... it's your call.... you might want to just fill it and take it for a test run...

I suppose that is possible, but I have no way of finding out. The previous owner bought it 2 years ago but never did anything with it. I'm thinking of flushing and filling it with mineral spirits to look for obvious leaks.

My advice is a little contrary to what most people recommend. But I can't tell you how many motors I've bought and took apart down to the bones and discovered that everything was in perfect running order before I started. Carb perfectly clean... etc

My usual approach now is to look it over and see if there is anything obviously wrong... check for spark.... and if It looks like it will run, put it in a barrel and fire it up.... You'll be surprised how often that works... You can always go back and do a tune up and further inspections... but the urge to do it all first has left me.... Those old motors were made to last... and are very low tech.... not that much can be "wrong"....

Thanks, All. I appreciate different options. It seems the consensus of opinion is to stick it in a bucket of water and fire it up first before tearing anything down.

Guy probably just drained it before storage. I always drain the gear oil before winter sets in.
Refill in the spring.
Tim

I flushed it out today with mineral spirits then filled it with the gear oil (man that stuff stinks!). No metal particals in the flush and no sign of obvious leaks as yet. The replacement recoil starter assembly is supposed to arrive Monday so I will finally be able to see if it will fire.