A rule of thumb is .003 gap for each
inch of bore. The gap is necessary
because the ring will expand when it
get warm. Too little is much worse
than a couple .000 too much. I suggest
.005.
Slim chance you’ll find the rubber grommet
except in another motor so you make one.
Search locally or on line for one and trim off
one side. Sticking it in a drill bit and then
removing what you don’t need on a grinder
works for me. Best get a few.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.