My experience with MKS pedals is that the outside of the pedal shafts corrode and wear; similar wear occurs inside the coupler. I found that if I kept the shafts well-lubricated, this wear could be minimized. I've always been a bit disappointed that these couplers, and their parts (springs, bearings, collars) are not made of stainless steel. Ditto the pedal spindles.


Here's a coupler disassembled. This is easy to do by removing a circlip (seen here enclosing the 4 retaining ball bearings). If the balls get too rusty, they can be replaced.



This coupler developed a couple cracks. There was a *lot* of radial play. There's no fix for this.