Did some reading on iboats, and found that exhaust and head gaskets could be a problem. Apparently there is some type of exhaust plate that commonly warps due to heat. Might look into that. I am not an outboard mechanic, so this is frustrating.
Literally dealing with this very same this on my fishing boat. I just upgraded to a 1977 70hp Johnson from a 1979 55hp Johnson. A long story short I ended up with water in the bottom cylinder. I got it home and started striping parts off it. I figured it was the head, nope. Anything after the head you have to get creative or just pull the power head to get to the bolts, which is what I did. Get the harness out of the way, same with the fuel, remove the bolt connecting the linkage with the shift shaft under the bottom carb, the beauty cover under the lower cowl, then the six bolts into the block and last the nut about 3" under the bottom spark plug. Remove power head, start with pulling the exhaust side. It is probably the gasket closest to the power head, that is where mine failed. The complete gasket kit is $65 for Sierra or between $80 and $100 for oem on ebay. I ordered the whole kit and will install all of them, after all, these seals are 40 years old, it is time. Have fun.