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If your window crank handles are like my 145, getting them off will
probably be your biggest challenge. You have a mirror-image example
of how it goes together in the passenger door.

I'm told the handles are held on with C-clips.

Gary

Body trim work is in the last chapter of Haynes manual for the 120/130/1800
models:

1. Remove 2 screws to armrest.
2. Note inner and outer door handle positions, so they can be put back the
same positions.
3. Depress handle escutcheon and with small screwdriver remove circlip
located between the handle and depressed escutcheon.  Withdraw both handles.
4. Remove 4 screws holding the upper turn molding, and lift away molding.
5. Carefully use a thin blade around the edge of the door trim panel to pry
loose the pop/snap-fasteners.
6. Lift away the trim panel.
7. If necessary, lift away the paper protectors over the holes of the inner
door frame.
8. Refitting is the reverse.

Cormac, step 3 is the one that is not explained well in the manual, but if
you can push the handle trim ring (I think it was black plastic?) against
the door panel, while pulling the handle in the opposite direction, you can
open up enough gap to see the fastening circlip hidden under the black
plastic ring.

Once you get the panel off (handle gently, it's old worn out fiberboard),
you can visually look at the window lifting parts, and you will see a length
of horizontal metal nearly as long as the bottom of the window.  On my 1800
(and I assume the 122), this metal strip has a U-shaped groove that the
bottom edge of the glass rests in.  This metal strip may have weakened from
age and rust, and no longer has a strong grip on the glass.  The grip is
reinforced by a rubber liner that sits inside the U-groove, which may also
be aged and cracked and no longer up to snuff.  Let's hope the metal strip
still has some life in it and will not require removal and replacement.
Replacing the rubber liner won't be a big problem.  With a new rubber liner
in place (purchase is cheap at any auto glass shop), set the window pane in
the correct position, it should take some firm pushing to get it seated.
After that, it will stay in place with the grip of the rubber liner plus
gravity pulling it down.  Also watch to make sure the window pane is in the
vertical tracks correctly, and slides up and down with ease as you operate
the crank.

Other than being gentle with old worn out fiber board and rubber components,
this is a pretty simple job.