first thing is to take the greasy cover and get it cleaned with TRI-CLORO the reason this is done is to remove any oil on the surface and to penetrate the casting and remove any oil or grease embedded in teh casting itself.
bead blast the covermake sure to get all gasket and paint off BE CAREFULL HERE you need to use fine media and be thorough you can hit the threaded hole lightly.
Ge the cover plated with nickle WITHOUT THE PROPER CLEANING and thats with tri-cloro the nickle will not adhere, this coating is 58-62rc and many many times harder than aluminum. Many guys have tried this in the past with ZERO success, it is all in the cleaning and make sure to mic the holes and tell the plater to build it up. MORE INSTRUCTIONS TO FOLLOW