I think this was discussed several years ago, it just happened to me, so I'd like to bring it up again. Over the years, I bought enough polishing gear and supplies to learn that it is terrible laborious and nasty job. So, when a nicely polished L-16 valve cover came up on Ebay, I bought it, even though I have 2 good ones to polish. When it was delivered, I was happy to note that it was a wonderful job, a very highly polished valve cover with no dents, holes or imperfections. It was as good of a job as I could ever do, if I started with a near perfect cover. Turning it over. I saw what they had done. They had abrasive blasted the piece first and the interior was full of blasting material! You DO NOT want this abrasive in your crankcase oil! I spent over an hour, removing the baffle and cleaning all the nooks and crannies of god knows how much abrasive. Over all, It's still a good deal, compared to the effort it would take to polish one myself. If you buy polished parts inspect and clean thoroughly before use!