Missed that, twice even.
So if I understand correctly, the interior handholds are attached by screws coming down through the cabin
top or deck?
First in this situation I would lean towards through bolting. Handholds can take a lot of strain when the boat is rocking and rolling.
Are the screws flathead/countersunk or pan head
? If flathead it doesn't leave much space for goop under the screw head
in the countersunk hole. If not already and it doesn't look terrible or create some problem I would go with pan head or truss head. Then still use a countersink bit to make a little pocket at the top of the hole to hold more goop.
I agree spinning a screw with sealant
isn't the best but I've had a couple of spots on my boat where I had no other option and still managed to get a good seal using butyl tape.
Last thing, if the previous sealant was silicone based you will need to clean the area well, probably sand it down some to get a good seal on the new install. Silicone oils from the caulk will penetrate the fiberglass
and even more silicone doesn't stick well to that spot.