After more than a decade......remember....
'Repaired' the top of the fiberglass tube with two part laminating epoxy with cabosil for thickening and milled glass powder for strength. It was really chewed up by P.O.'s not seeing the setscrews and wrenching the cap off without backing out the screws.
Shoeshined the repair smooth and fair after it hardened with sandpaper - making sure the cap sat tite and square on the bearing without a wobble.
Find the sweet spot for the cap, probably easy/visual access to the 3 set screws, and mark exactly where the screws will hit the tube when screwed home.
Then drill a slight depression in the tube for each to seat in. If the set screw has a point, then a drillbit can make a perfect seat. Don't drill deep, or you'll have to fix it again.
With 3 set screws, it's probable that that one won't get a seat given the angle and shortness of the tube in the cockpit. That screw will be out of sight, but I would try to gouge in some sort of slight depression (rat tail file) so that all three screws are working and the cap is secure.
Can buy 316 set screws of may styles and lengths at McMasterCar.com
imco