I have a very old mercury 60hp outboard (1959 or so) and have no idea what to put in the lower unit

 any help would be appreciated

   Bass Smacker

 

Are you asking about lubricant?

You can get a tube of lube from a dealer at some rediculous price or go to you local auto parts store and get a quart of Penzoil 100% synthetic gear lube, something like 85 - 90.   If you don't get the synthetic, make sure it's  rated at GL-5 specs.

On units like that, there are typically two access screws.  So if you get the loob in a toob it may be a little more expensive but it is 10 times easier to fill.  I remove both plugs and let it drain, then put the tapered nozzle of the fill tube in the lower one and squeeze until liquid arrives at the top hole.  Put the plug in the top one and then you can remove the tube without it running out as you put in the bottom plug.