[HPsauce]

Here is a summary of the procedure. I did a lot more than this and you may need to as well, depending on the state of your mirrors, doors and wiring.

1. Fold mirror, remove small phillips screw that is exposed in a recess in the end of the non-swivelling section (it helps hold the plastic trim in place)

2. Open mirror, remove plastic panel on bottom (2 screws) and then take off the glass (I used a plastic ice scraper to lever it).

3. Lower window. Remove the mirror cover - take out 3 (T10 or phillips) screws visible around mirror glass mount then wiggle it off.

4. Remove interior triangular trim to expose mirror mounting bolt, the trim is held by just one central push-fit clip and pulls off straight inwards but may need easing round/over the top of the main door trim.

5. Undo and remove bolt and washers from inside - mine required a T45 Torx drive.

6. Work mirror free of rubber seals and peel away foam pad to expose 2 screws on the back of the long edge of the triangular metal mounting plate.
You may need to disconnect the electrical connector to the base of the unit depending on the amount of slack in the cables.

If you have mirror memory there will be a secondary cable that goes through the door mounting and down behind the main door trim panel. If that has insufficient slack the panel will have to come off and the cable freed or disconnected, but try to avoid that if possible. (see note below, it doesn't have to come totally off)
(If your mirror remains attached to the car don't forget to protect the paint with a cloth or towel.)

7. Undo the two remaining screws that hold the exterior plastic trim onto the metal mounting plate. The 3rd screw outside near the pivot was removed in step 1.

8. Loosen the trim and manipulate it round (you can't take it off) until you can see the bottom of the main pivot. Turn the mirror unit so that it is upside down with the pivot (possibly only partially) on view.

9. Liberally lubricate the pivot around the edges of the metal rings with WD40 3-in-1 oil etc. ensuring plenty runs through to the inside of the inaccessible gear mechanism. Don't pour oil down the centre hole where the cables run, that will not go anywhere useful.
(make sure you have paper towels or similar to catch any drips)

10. If you can connect the main electrical connector, preferably while still inverted, "exercise" the pivot by folding and unfolding electrically. Initially a little manual assistance may be required so someone to operate the "fold" switch on the drivers door is useful while you support and "encourage" the two parts of the mirror unit. You may find it best to have the engine running as the voltages will be a bit higher to the "fold" motor.
(don't forget to put the plastic cover back roughly in it's rightful place first or it will block the movement)

11. Alternatively remove the unit completely and "exercise" it with a suitable 12v (or slightly higher, 14v or 15v) DC supply. The relevant pins are numbered 8 and 9 on the main connector. One polarity will open and the reverse will close.

After sufficient "exercise" the lubricant should have softened the grease and dirt blocking the gear mechanism and it hopefully will run smoothly in both directions. When you're happy reassemble in the reverse of the above sequence. Exercise it a bit more once fitted to ensure it's all OK.

Note. If you do need to remove the door card to disconnect the long secondary cable (for memory) you may get away with only doing it partially; I did.
The cable (on mine anyway) runs down the front edge of the door and the connector is not too far inside but near the bottom.
I managed to get at it without having to lift the card over the locking button or unclip the rear edge, doing the following:
Remove decorative trim (it levers out gently starting at one end) and 2 of the 3 screws behind - you can leave the rearmost one in place.
Release rubber trim and remove screw below (if present) at top front corner.
Remove handgrip trim and 2 screws behind it. (You might just get away without doing this)
Pop clips open along front edge and along bottom as far as necessary to gain access.
Small hands definitely help!