Re: At least the O-ring wasn't frozen this time...
Pre late '80s or early '90s Johnson/Evinrude small single cylinder outboards in the 4 to 6.5 hp class (sometimes called sailboat pusher motors) have a copper water line from the waterpump down by the prop up to the powerhead. The connection between engine block and tube is sealed with a simple o-ring. When the engine is run, the o-ring gets wet. When the engine is shut off, the o-ring dries out. Leaving behind anything dissolved in the water. Especially salt, if the motor is run in the ocean.
These deposits build up over time, gradually putting pressure on the o-ring. Either the iron block, or the soft copper has to give. The copper loses, of course. So eventually, the copper pipe is pinched off, and the engine no longer gets fresh water, and so it overheats.
The fix is simple. Remove the copper pipe, heat it up, run a mandrel through it to pop out the pinch, replace the o-ring (a 19 cent part) & Bob's your Auntie.
Unfortunately, R&Ring the pipe involves pulling the entire powerhead, which is just short of a complete engine overhaul. About a 4 hour job. At $165/hr shop rate. Plus any parts that may need to be replaced because they are too worn to be reassembled.
Bottom line: It can cost well over $1,000 to replace a 19 cent o-ring ... on a motor that is worth maybe $500 if it runs well and looks pretty. And that is from an honest shop.
Bloody O rings indeed. This round's on me.