I can think of a couple options, since you are putting on a Keel Guard.
1) Remove the brass strip entirely, filling the holes with thickened epoxy to seal them off (the KG will keep UV from the epoxy).
2) Re-secure the screw(s) and leave the strip in place.
I did #2. I figured that I might add a KG later, but knew that I might not, and/or it would be in the more distant future, so I probably did it more thoroughly than you want to, but this may give you some ideas anyway.
- First I removed all of the brass screws (I did half at a time, since I wasn't removing the brass strip) and poked into each hole with an ice pick. I wanted to see if I would hit solid resin or poke into the boat from a too-deep hole. I hit solid material on all of them, but still wanted to be sure, so...
- Next I cleaned out each hole with solvent/pipe cleaners/etc. to make sure the new epoxy would adhere.
- I ordered new fasteners. First of all, I have a 'thing" about flat headed screws in places where there is no bung over them (so I ordered oval heads); second I ordered them just a wee smidge shorter, so there would be more room for thickened epoxy.
- Taped off all around the holes.
- Cleaned the fasteners and the holes with solvent, and then put a "worm" of butyl tape around the underside of the head on each fastener.
- Mixed up some neat epoxy and "painted" the inside of the holes with a pipe cleaner.
- Put thickened epoxy in the bottom of each hole with a syringe (just a bit, as what I was aiming for was thickened epoxy in the bottom of the hole and partway up the screw threads, then butyl around the head of the screw and in the chamfer).
- Installed the new screws, then cleaned up any overflow.
Sunbeam