Another check is the pintels themselves.
I found on 1182 that they came loose after a days sailing, even a half day in windy or in a large swell would loosen the pintels enough to allow a visible amount of sideways movement in the blades and rudder cases themselves.
I changed the nuts over to ny-lock style nuts and still had issues for several more races
I eventually added a 1.5mm stainless plate with 2 holes for the bolts in each pintel and discarded the washers in an attempt to tighten it up.... this did help considerably but it wasn't until I went up a size in the bolts that I saw some relief in sight
Now after several months everything seems to have settled down and the pintels aren't coming loose any more
I think the culprit may have been a dry transoms that got wet and expanded then dried then wet etc etc etc and the bolts were simply crushing the timber as each re-tightening was performed.
Something related to an older boat that's been sitting around in the weather for an extended period.... sound familiar
stab in the dark but if all the other suggestions fail ......