Rudder "Liposuction"
Back in the 80's, we had to repair a weeping crack in the leading edge of the large transom-hung rudder on our Niagara 26. I took the rudder home one autumn and propped it up in our garage for about four months. I drilled one 1/4" hole near the bottom and water dripped out. So I drilled a bunch more up 'n' down the blade. Above a certain point there was no dripping.
It sat there and oozed water slowly for a while, and then slowed to nothing finally. Not being very good at delicate glass work yet I took it in to a local boat builder to have some thin cloth applied after the gel coat was sanded off. It came back nicely re-faired and ready for finish.
I used LPU paint for the above-water part and the usual (at the time) VC17 for the lower blade.
Never a repeat of the problem.
That was a foam rudder blank inside of a molded-out frp shape, too.
As I recall, I also epoxied in the holes for the gudgeons and re-drilled.
My guess is that you can drill all the holes needed, and just plan on epoxying them in later. That's if you are taking the rudder off for the winter or at least leaving the boat out of water for awhile.