upps and i just bought ur spare.

has this happend gradually or just recently

smacks to me of high oil pressure. could be a number of things
engine has external oil return pipes, one of those could be blocked, kinked whatever causing oil to gather in the heads. oil pump could be on its way out and not pumping enough oil and wet sumping. could even be overfilled with oil.

ive got a complete engine thats stripped down into bits, give us a call if u need any help or bits m8 uv got our number and happy to help (y)