On the car, I had purchased one from the local parts house, and it was a steel piece. A, it didn't work worth a damn, and B, it rusted all to hell in a matter of months. Spilled dot 3 on those eats the paint and they rust quick, but that's another topic. So when going to swap the MC's last night, I was trying to salvage the rubber retainer (Trying key word) and when checking the new aluminum one there was no resistance when I put the rod in. Of course this was all done on the bench, so taking a flashlight, and a scribe, I looked at the back of the piston, and it was smooth machined to the cup at the bottom, whereas, the steel one had been machined for the retainer. It is obvious when you compare the two. I think I'm going to disasseble the steel one, and see if the piston is swapable, and maybe that will solve my problem. The only other option I can see it to remove the piston and go and have it machined for the retainer, but what a pain in the butt, and cost, that would be. I guess I'm looking for the easy way out, but sometimes the easiest isn't always the cheapest, and vice versa. Oh, and yes mine is a manual brake car, and I was told that it would work with my setup. No mention of the retainer though, either by myself or the seller. I didn't think to ask at the time. Now that I am doing the swap, I learned another interenet parts buying lesson. You gotta ask the right questions before you buy from here, ebay, or anywhere on the net, because if you don't than it's going to bite you.