Christian, I personally have never had problem like that. I have also ordered rear mains from two different sources and they all look the same as if they are coming from one source. The seal is a flexible rubber that normally snugs around the extension of the crank shaft. It also has a spring wire inside it to hold it snug. It normally only goes one way and it's real simple to install once you pull the transmission. I don't see how they could mess it up. There is a front and back view on the site. Here is the link.http://www.specialtauto.com/clutch-comp.shtml John Hervey << I suppose they could be right, and I'll just have to live with an oil puddle in the garage, but I'm hoping that they're wrong. Has anyone had any experience with rear main leaks that don't seem to go away? Any solutions? Do you recommend any oil additives to try to plug the leak? Do you recommend that I stay far, far away from leak sealer additives? Are there any tricks to installing the seal that this shop may not know about? >>