Rutger,
To your first post: what you are talking about is "old fashioned" u-channel window felt/guide. Some years ago, an enterprising MB reseller decided that the whole OEM window guide concept, where instead of the glass sliding in this felt-lined u-channel, they used metal glued to the glass and sliding in a greased steel u-channel, was problematic. They started selling the old u-channel felt guide.
The use of the felt guide involved gluing it to the inside of (once greased but now cleaned) the steel u-channel, and eliminating the metal guides that were once glued to the glass and ran up and down the steel channel. I bought into the concept once, and tried it on my driver's door.
Big mistake, IMHO, as the glass wobbled when at the top. The reason for this was quite simple: the felt channel offered very little support of the glass on one side, perhaps 2-3" or so. That was not enough support when the window was up. I could flex the window +/- 2". I bought window guide repair kits, cleaned everything up, and made it normal again.
The real problem is that adhesives 40 years ago were not as good as today--by redoing the OEM window guides with modern adhesives they'll work better.
The reason why I took the whole door apart in the first place was a rattle when the window was down. Most suggested that the guide had fallen off and was rattlling around the bottom of the door. In my case, what happened was the bottom of one of the arms that move the glass was contacting the bottom of the door when in the full down position because of a missing stop. Once a stop was added the problem went away.
