Bringing this in for a landing......
It was the shift cable. It was crimped just above the bracket where the cable end and transmission lever meet. How it got crimped, I haven’t a clue, but it happened after I took it out of the water last fall. The shifter worked silky smooth all last season. I’m very aware of the potential for damage to the cable and I’m very careful around it. There was an enthusiastic guy who worked in the engine compartment and he may have inadvertently hit it. It’s easy to do. Who knows.
I’m in Tarpon Springs, Florida to cruise a section of the Great Loop. Scott’s Marine graciously worked me in. The first step Scott’s took was to see if the crimp could be straightened and cable freed. No joy there. The local West Marine had the appropriate cable in stock. The original cable was 21’ and Scott’s Marine recommended using a 22’ cable to route the cable using a less tight radius to the transmission bracket and to position it so that it’s less likely to get crimped again.