i media blast for a living, couple years ago i bought a vapor blast cabinet that works well for aluminum. i have done a few transmissions with good results. its slightly brighter than OE but will fade over time. The finished surface is not open like a fractured abrasive will do so it will not oxidize over time. Not saying this is the best way as the keyboard experts will chime in that is some how wrong but one option for you if you have anyone local to you with a set up. You can google or you tube search for examples