Thanks so much for all the replies. My particular motor is a 1966 Johnson so it is definitely prone to the early model issues.
A short background - It was acquired by my brother-in-law - he bought it from a widow on his mail route just because she asked him to. He's never been one to fish or boat so he put it in his barn for about 20 years. When I got a jon boat about 10 years ago he passed it on to me.
I've used it 5-10 times per year since then. Beginning this year it has been hard to start and has been running poorly at anything over a slow speed.
I've never used anything but ethanol free fuel along with putting Stabil in the fuel.
I've had the carburetor off, disassembled and soaked in acetone followed by spraying with carb cleaner then blowing out with compressed air. I put in a carb kit (including removing and replacing the core plugs), removing the fixed jet (after I finally got a proper tool for that), replacing the float & needle. I also replaced the packing and washers on the slow speed jet. That jet had just a very little bit of wear on the part that seats (the "pointy" end) - but it didn't have a groove.
It seemed a bit better when I tested it in a barrel, but when I went trout fishing last weekend it was still hard to start and at one point was missing badly. The river was so low I was unable to try to run it fast (plus I had one of my adult sons and his friend with me - we weren't going to go fast anyway)!
Odd thing is that once it is started and warmed up, it starts on the first pull. I plan to try again on adjusting the slow speed jet to see if the starting improves. After that I will start working on trying to see if I have an ignition issue (plugs look OK although the top one is a bit damp with fuel -
not a lot) compared to the bottom plug).
Compression seems OK based on what I've read on LeRoys Ramblings (great info - as well as what I've watched that cajuncookone has done) at about 73 psi on both cylinders.
Also I will start focusing on the areas it can leak (certainly appreciate the pointers in the messages sent about that). I'm not much of a mechanic but I think leak spots 2 & 4 can be eliminated. I replaced the water pump a couple of years ago so those seals should be OK (I replaced the impeller a couple of weeks ago & they seemed fine then). From what I can see by just looking, the exhaust hose (#43) is OK. I'm not sure how to check the shift rod boot - l will pull the lower unit and see if I can spot it and tell if it is there and if so, what kind of condition it's in.
Thanks again to everyone for the input and the links - the PDF's are great and the part numbers really helpful.