you converted to jap because you couldn't handle the almighty power of the RS's

Its an easy job really, loosen the cam pulley bolt, slacken off the cam belt tensioner, remove the belt, pry out the old seal with a screwdriver carefully.

Refitting it will be tricky as you need something big enough to fit over the end of the cam but still small enough to push the seal fully home. I had a right mare doing one years ago, then my mate had the best idea, i don't know quite where the inspiration came from, but a T2 compressor housing was the perfect size