viton corner seals (93 FD)
 

Was surprised to see rubber used in the round corner seal when dis-assembling the engine. Is there a source for a viton corner seal to take the place of the rubber one???
have a 93 R1 BTW

No, just the stock mazda rubber one. I never replace them in rebuilds, they have no impact on the running of the car. They harden before 10k miles have passed, yet the engine runs the same for 100k.

You have the option to use aftermarket solid corners, which are far stronger.