It took me a while to figure out. I'm working on an 48SD. The piece goes onto the vertical window channel at the back of the door and then into the lower channel on the window. I cleaned both channels with brake cleaner then applied a very small amount of grease. Too much grease always attracts dirt and eventually clogs things up.

I never did find a really good way to manipulate and hold the window but eventually everything lined up. I'll call Peach & see whether they can get alternatives to what they list currently - OE parts and URO. OE is too expensive.

I expect that part is missing from the other doors because I've never seen it and have had window regulators out. Now onto the next project.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.