Cobber

You may well find that the oil seals are generic, look for numbers on the face of the seal, beeter still take the seals in with you, go to an industrial bearing supplier, drop 'em on the counter and let the counter jumper see if he can find a suitable equivalent.
A gearbox designer would have to have some very specific requirements to bother with a custom seal when there are plenty of more cost effective, standard off the shelf seals that would do the job.