Neptunes are for the most part well-built. I would check for spark and clean out the gas tank and carburator, then put new grease in the lower unit.  Like most outboards, if it has spark + compression and is complete it will probably be fixable.

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Aidan Smith

I have not had my motors for a long time, and only just got around to getting grease.  Previously, I had used oil just to test run them with the intention of later getting grease.  I ordered some of the John Deere Corn Head Grease and I intend to use this in my motors due to it’s availability.  Hypoid will leak out faster than you can replace on outboards unless the lower unit is specifically labeled for oil.  that Johnson you have probably takes hypoid, and if it does, it would be labeled on the lower unit by the fill hole.  I have a 1945 Neptune 2 hp and I used oil in it just to test it and it is extremely leeky even with a new gasket.  That is why I am switching to grease.  From past forums, I have read that John Deere is supposed to work well.  I would rather go with a grease that I heard works well than general purpose grease, as general purpose is probably intended for lower heat situations.  John Deere Corn Head Grease as well as any sort of trailer bearing grease would probably work better, as they are intended for higher head purposes such as an LU gearbox.

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Aidan Smith

I could not find gaskets for my Neptune at the time I was fixing it up a few months ago (or gasket material was way cheaper; I can’t remember which).  If you buy gasket material and cut it yourself you can probably save some time searching for gaskets as well as some money.  To get the grease in, I would take off the prop assembly, pack in grease, then put the prop assembly back on.  After that, you can take a grease gun and inject it through the grease LU hole while turning over the engine to make sure no spots are missed.  Gasket material is cheap off of Amazon or Ebay, but buying premade gaskets for rare-ish motors such as Neptunes will end up costing a lot of time and money to find when you could buy some material to last you through multiple motors.   You also then have gasket material on hand and do not have to wait for premade gaskets when you get another project and want to get it running.