After all those encouraging replies, I guess I could give it a new go.
As I said, three installs didn't help. I had been using SH3CMDR but not on those last two tries.
I do admit that I didn't actually delete files, just used the 'repair' and patch routine. There may have been some bad old stuff left behind.
Thanks guys, the captain is back on the bridge. Just because the diesels won't start, the batteries are exhausted, and the food has gone bad - no reason to abandon ship. We shall overcome.
I will report back if the radio still works.