Hi Andrew
I think this is the old cookie for those of us who sail on salt water at some time and don't realise the need to disassemble the blade from the stock on an annual basis to grease up the bolt through it's sleeve, or so I understand.
I have had a bit of a problem with this recently and have managed to improve the situation slightly using liberal amounts of WD-40 and silicon spray. I did try some heat (from a weak gas blowlamp onto the end of the thread) but to little avail. I also tried some hammering to try to extract the bolt but this also failed for fear of damaging the stock.
At the present time the rudders go up and down fairly easily but I think the sleeve must be rotating in the blade, rather than the bolt rotating inside the sleeve. I know that at some future point I shall have to saw through the bolt on each side of the rudder blade(s), inside the stock(s) as recommended by George Carter.
I understand that the latest replacement bolts/sleeves do not corrode together in the same way.
Here is a post on the subject which I found using "hacksaw" as a keyword:
http://www.sprint15.com/forum/viewtopic ... ht=hacksaw
Regards
Robert.