80 Series LH Door Window

Yep, easiest thing to do is pull the glass out of the door.
This way you will be able to work on it more easily.
You will fine a Philips head screw under the door rubber at the top of the Quarter glass, there will be a couple(going by memory) 10mm bolts that hold the upright felt channel in place that goes up to the screw you have just taken out.
The rubber around the quarter window will come out with the glass.
Pull the quarter glass out, rubber and all, you will now be able to get the glass out through he top of the door.
I cleaned the bottom rubber the the glass sits in and use windscreen silicone to fix the glass to the bottom channel, some times the rubber shrinks a little, this lets the glass come out.
Mine happened while it was raining Cats & Dogs.
Once you have the glass out, you will be able to work on it.
It's not to hard of a job to do.
It's just an age thing, my old girl turns 21 in December.

res.q.guy - Removal of window glass is a vital step, you can't operate properly inside the door cavity.
I've always found that the best technique is to remove the rubber from the channel, clean the glass, the rubber and the channel section thoroughly - then glue the rubber to the glass, then coat the channel with glue, and push the channel section over the rubber.
Needless to say, ensure the glass is supported by carpet, heavy cardboard or some other suitable medium that will prevent damage to the glass, when you're working on it.

Cheers - Ron.