I’ve got a Kart Mini(Riomar) shifter that I am rebuilding the brakes on. The front calipers have x-rings that sit inside a groove in the caliper bore to seal against the piston. The rear has o-rings installed that were probably put in by the previous owner since they are much easier to come by. The use of o-rings concerns me due to the fact that they can roll or twist. I like the idea of using the x-rings since they would offer a double sealed surface while being much less likely to roll, but I am having a difficult time finding them in EPDM. I can find them in Viton or Buna N, but this would require switching over to DOT 5 fluid. I am skeptical about doing this as I have heard that DOT 5 can produce a spongy pedal, especially when hot. I think it will be much easier to find some square cut o-rings in the proper size and material than it will the x-rings, so would these be an acceptable replacement to the current x-ring/o-ring set up I have going on right now? Any other suggestions or opinions?
I should also add that I have tried sourcing rebuild kits, but apparently there is not currently a distributor for these karts in North America. I tried contacting one of the former dealers with no response and have even tried to make direct contact with the factory in Brazil (through email with the use of a text translator since I don’t speak Portuguese), again with no response.