Jerry,
Some times the felt just works it way out and falls to the bottom of the door. I lost mine.
My drivers side window would rattle and come out of the track, so I took of the door card and found the rear track laying on the bottom of the door. I removed the holding bracket, just one screw, and saw that the tack welds holding the bracket/track together had broken loose.
I drilled out holes in the bracket and the track where the tack welds had been and used pop-rivets to repair the unit. I could not find the felt, so I made a new one. This gets tricky, so I will try to make is simple.
I had some 1" wide sticky back smooth velcro, so I cut a piece that would fit in the bottom of the "U" track and worked that the whole length of the track. Then I took another length of smooth velcro and laid that into one side of the "U" track and then folded it back over the metal edge of the track. That left only one side of the "U" track as bare metal. I could tell that just laying in another velcro edge wouldn't hold the window in place, so I used some sticky back foam insulation material about 3/16" thick and 1/2' wide and laid that into the inside of the of the "U" track.
I then rolled the window all the way up, laid the top of the track into the the opening at the bottom of the window and remounted the track with the single screw, getting it as close to the original position as possible. Now there are four guides in which the window rollers ride. I used my little finger to work grease into those guides and then rolled the window down, and greased the other ends of the guides. I worked the window up and down several times and checked the guides again, add more grease as needed. Lastly, I worked a very small amount of oil into the new "Felt" I had made just enough to have the window slide easily in the track.
I put the door cards back on and test the window again. I noticed the next day that about 80% of the rattles in my car had gone away.
Since you are working on the windows anyway, if you want to fix the problem of water dripping in right at the edge of the top and the window frame where the window meets, I have an answer for that. After driving to work in the rain I had noticed a puddle of water on the passenger side floor mat. When I got home that night I inspected the doors and found that a PO had put a big wad of black goop on the side window frame right where in intersected the top. Well that wasn't very pretty!
I went to Home Depot and bought some sticky back insulation about 1/4" thick and 3/4" wide. When you open th door you will notice that the side window frame has an edge that sticks up about 1/2" and in the inside of that edge is a perpendicular face about 3/4" wide. Lightly sand that face. Being careful not to stretch the insulation, run a length of insulation the whole length of the frame from the rubber window stop to the edge of the door where the frame goes into the door. Press the insulation down so that it makes good contact. That should keep the water from working it way into the car and I noticed that it will greatly reduce wind noise at 70 mph with the top and windows up.
Have fun, drive fast & safe, be kewl,
jclay
