I'm not familiar with the RV12 set up....with that said, I would pull brakes off again and look for loose rivets, cocking / sticking of the brake pins first. Also look for any obscure cracks in any of the supporting brackets. I use an LPS spray product (can't recall the number right now, but it is not the normal 1,2,3 that we all use liberally) on the brake pins and back side of the plates. It drys to a dark grayish green color and is a high temp, dry lube. This particular lube was specified in my Grumman Tiger Maintenance Manual....and as I recall, one can cost almost $100! I'm hoping one can will last me almost a life time..... I've used high temp antiseize on the pins in the past with good success, but it has the potential to give other problems as opposed to a dry lube. Check too, while you are at it, that the master brake cylinder is coming back fully unloaded when you take your foot off the brake. Some brakes will drag when the pedal sticks not allowing the master cylinder to fully unload. If all this is fine, then I'm thinking the next level of check is the piston in the caliper. Sometimes it can get cocked or have a bit of debris causing sticking....I have seen this happen once and in my case, I simply pressed the piston more fully back into the caliper (watch doing this because the fluid level will rise in the reservoir.)
Hope this helps .... at least a little maybe.
Ellis
RV7a Finish Kit, A&P/IA