So I need to deal with the gasket on the rear door of my minivan, which has degraded and leaks. Examining what's worn out, I see that this isn't the relatively simple "generic" rubber gasket that I found online, but one with funny-shaped bits on it at the top to cover the join between the two doors. I went to the local GM dealership and showed them what I needed: it's a Left Door Gasket for a 1989 Chevrolet Astro. They can get it from the warehouse in Reno, and it will be here tomorrow or Monday. $170! Yikes! That's about three times as much as I expected to have to pay. I sure hope it is not too difficult to install.