The 340 is similar to the 310 WRT the master cylinders at the top of the pedals.

I think its a combination of a few things.

1. Yaw in a 340/310 on roll out (and TO) makes favoring the right brake happen more often. Then the right caliper warms up a lot more.

2. taxiing for some reason favors the right brake also. I try to adjust thrust so it tracks straight, but there's lot to do on the way to run up.

The right brake eventually heats up more often than the left. This makes the pads swell a little more than the left and you may even hear it when you tow the plane around after landing.

Hot brakes makes the orings swell and the fluid down near the calipers is a lot (Darker) funky .

At each annual, its a good idea to push out ALL the brake fluid and then fill from the bottom with new. Its scary how much 5606 can turn to sludge.