If this helps any of you with your decision, being around the trucking industry all the these years, we are always needing maintenance. One thing that is most expensive is rear differentials. We have two in most cases. This upgrade to your car will strengthen it to last forever. It takes out the weak point. If you lost a rear end playing around, drifting, drag racing, doing a burn out, whatever, it will cost you more to repair it than this upgrade. Any good repair shop can install this part in the diff once it is built and perfected for install. These were all questions I asked, and was assured would take place. As for the money, Devon assured me, nothing is billed to your card until the diff is perfected and built, the second payment isn't billed until it is shipped. I am happy with that. My concern was being billed before a perfected product, and that isn't the case...if you are keeping your car, and you like to drive hard like I do, this is a part more important than any other upgrade you are thinking about...bar none....