This has been an ongoing issue since day one....

Initally I was sheering the bolts that held the bottom pintels in place, so I simply added a backing plate to the inside of the transoms and this did for a while work.....

then it started to happen again, the bolts were often loose after a single race and a simple half a turn sorted it, but eventually I started to sheer bolts again.
Next step was to upsize the bolts and this stopped the pintel issue instantly but that's about the time I saw the rivets being stretched and becoming loose.

In high winds the problem was worse, a single race would mean atleast 2 rivets being lost per rudder case, ultimately at Lake Bolac in the very strong winds we had the 3rd rivet failure which resulted in the previous pics.

time for an upgrade of this