That seems to be fairly typical of the rudders at the time. Mine (2001 40 Ocean) had similar issues. The water got in at the top where the rudder post is surrounded by GRP. The rudders at the time were not built by Jefa, but by JP3 - beware of blindly relying on the Jefa plans, which are nice and correct for their replacement rudders, but do not necessarily correspond to the JP3 manufactured original rudders, at least not exactly. This mistake has cost me an extra week in the boatyard plus several hundred quid.
The best way to dry out the rudder is to put it upright, drill a hole or three in the bottommost part of the GRP and let the water drain out over a week. Upon doing so, I discovered evidence of previous drain holes. Shelter it from rain. Once reasonable dry (you'll never get all the water out as the rudder is filled with foam), seal the holes with some thickened epoxy, or if you like glass it. Mine also started blistering
after being laid on the side (no blisters were apparent before it was dropped), so I repaired that as well and finally gave it two coats of Interprotect.
Then, and that's the important part, grab a Dremel and cut an angled groove into the GRP, all around the post. Clean it out with acetone and then fill a flexible sealant (Sikaflex 291i or 3M 5200) into the groove, to prevent future water ingress. This is also what Jefa recommends (their new rudders already have it in place):
ftp://ftp.jefa.com/rudder/maintenance/Rudder_blade_anti_fouling_instructions.pdfThis is how Jefa makes their rudders now. Interesting to watch in any case:
https://www.youtube.com/watch?v=HqBXDuI5NzY
