I finally bought a pair of new wing mirror glasses at the weekend, whilst fitting them I noticed neither mirror would adjust.
It has always been a bit hit and miss, one day they work then they don't. Eventualy one side started to work, but nothing from the other. I thought it was the adjustment mechanism, but it was not.
After a lot of sodding around with the mirror mechanisms with no improvement I took the switch out of the drivers door, and took it apart. Mines a late car but I would imagine the same could easily apply to early ones too.
Basically there is a small printed circuit board which the moving contacts of the switch have to connect to. The copper on the board was very dirty with what looked like burnt on grease all over it. Using brasso I polished the contacts up to a bright shiny finish. I reassembled the switch and both mirrors now work perfectly!
This took half an hour to do, and I highly recommend giving it a go if your mirrors do not adjust.