I'm with all the others. Get it fixed before you reslip. Had one rudder delaminate once when under spinnaker
If you get more water out when its warm, then why not create a 'oven' using a heater and wood frame / plastic covers and really get it dried out?
I don't want to be alarmist but also suggest you might want to check out what form of core
is inside the rudder as well. A wood core
may have been damaged by so much moisture.
Drilling more holes and circulating warm air will help get the moisture out - as would some form of vacuum bagging if you could arrange it.
Once fully dry and you also happy with the rudders structural strength, you can as suggested plug
all openings with epoxy
putty, fair off, repaint and refit
Its not as hard as it might sound.