Fuel pump did NOT solve the problem, but I did! Drained the fuel again today and almost immediately it trickled down to a drip….. Let it take it’s time and when dry, pulled the bottom fitting. Sure enough, ANOTHER piece broken off gas cap when someone tried to remove the lanyard. This part had a nipple on one side that was just the right size to plug the outlet. Of course it is too big to come out the bottom, so had to pull the tank and shake it out the top!
Well at least now I’m confident there is nothing else in there! No wonder the previous owner wanted rid of it. Hopefully, mad perseverance pays dividends?