It's too late now but for future repairs take a look at Diseasel300's replacement sliders. He had some made up but he might be sold out now. He was talking about making some more.

The "Diseasel" - '86 300SDL

Another way to go which eases replacement. Thanks, Warren!

W126 rear window won't go up

Both of these repairs have the added advantage of not having to remove the regulator assembly if future replacement is required.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now