Tom, I had the same problem with the OPP top. From what I hear these tops are the first thing to **** out on these pumps. I wanted to keep this pump as close as I could to original so instead of using a repro plastic top I decided to repair the original. Here's what I did:
REMOVE THE ROTTED INSERT THEN SANDBLAST
I THEN CUT SOME HEAVY FIBERGLASS CLOTH INTO STRIPS
USING POLYESTER RESIN I CRISS CROSSED THE LAYERS ABOUT 4 OR 5 THICK
NEXT I CUT A PIECE OF 18 GAUGE CARBON STEEL SHEET METAL TO THE EXACT SIZE OF THE INSERT, EPOXIED IT IN AND THEN LATER LAID 2 MORE LAYERS OF CLOTH TO HELP BOND THE INSERT TO THE TOP. I THEN DID THE BONDO / SPOT PUTTY THING TO THE EXTERIOR
I THEN DRILLED OUT A HOLE (ABOUT 50 THOUSAND HOLES IT SEEMED LIKE), TOOK A 2" GRINDING ROLLER THEN MADE THE HOLE ROUND
AFTER THE PRIMER, SANDING DEAL IT WAS EVENTUALLY PAINTED AND CLEAR COATED
I know there are many ways to repair things, this is just the method I chose here which worked out well for me.
Neal