O.K. so I went and done it.
I followed someones advice and removed the door card/panel; disconnected the door speaker and the mirror connection. Removed the vapour barrier and the bolt which doesn't seem to do anything. Great. BUT remember if you remove the door panel, you have to replace it!
This is how to replace the door mirror innards.
First get prepared. You will need a 10T torque driver. A Phillips/crosshead screw driver. A flat lever to get behind the mirror glass and a nice big microfibre cloth or something similar.
Park the vehicle where you will be able to get at the mirror comfortably and place the cloth below the mirror unit and tie the top ends around the base of the mirror. This could help stop damage to the paintwork.
As you could spend some time holding the mirror unit in one hand and doing the work with the other, place your tools where you can get at them. I emptied my left hand trouser pocket, so that I had somewhere to put the screws as I removed them. They are needed for reassembly.
At this point go to the rear of the car and disconnect the battery. (Unless you really want to remove and refit the door card!)
Press the mirror glass inwards at one side to allow the flat bladed tool to get behind it and gently prise off the mirror. It may come off in one go, or you may have to repeat this in more than one place. Place the mirror somewhere safe. If the mirror has two small tags on the back of it and there are a couple of spare black wires hanging, you have a heated mirror.
Remove the four 10T torque screws which hold the casing together and place somewhere safe. Pull apart the two halves of the mirror casing and place somewhere safe. Remove the four cross head screws which attach the motor to the mirror and pull out the four wire connectors from the rear of the motor. They are marked (on the motor) Black, White, Blue and Brown. Two of the connectors may have two wires going into them. They should be black and have their own connectors on the other ends. These fit onto the mirror glass. At this point you should be left with the metal innards of the mirror unit in your hand and the base of the mirror attached to the door. The two being held together by the mirror wiring. Think about what you are doing and gently draw the wires through the holes in the metalwork. Once the wires are out, dump the metalwork. You now have the base of the mirror attached to the door and a length of cable sticking out of it.
The base is held to the door by two allen screws. (In my case the inside of the base had been filled with adhesive and I could not see the allen screws. I had to chip the adhesive away with a pointy thing.) Remove the allen screws and lift the base from the door. Before pulling it over the wires, remove the rubber seal from the bottom of it and leave it on the wires. Remove the base taking care not to damage the wires.
Pull the seal a little way down the wires and use your favourite car cleaner to clean the tear shaped dirty mark from the door where the mirror base had been fitted.
Re assembly is the opposite of what you have done to take it apart.
Thread the wires though the new unit. Fit the seal to the bottom of it. Four lugs fit into holes in the seal so make sure that the do. Fit the two new (provided) allen screws. Connect the wires into the back of the motor. (It has TOP cast into it.) Position the two black wires where you can get at them and refit the motor using the four cross head screws.
Put the outer casing into position and make sure both sides line up. Fasten them together with the four 10T torque screws. Do not us superhuman strength. You are working with plastic.
Fit the two black wires to the back of the mirror glass and press the glass into position. It presses onto four cast clips. If it doesn't hold, remove it and try again. When you are happy with the glass attachment, open the door. Place your hand gently around the mirror unit and over the glass. Slam the door. If the glass falls out, your hand should hold it. If it doesn't fall out, you should be alright for dealing with pot holes. Reconnect the battery.
Job done. You may have odd mirror bases. The ones that come are black, or at least mine was black. It is a Z3 so it is pretty ancient and the remaining original mirror is the same age as the broken one which you have just replaced. It might be a good idea to replace the other one and you get 10% off.
That is the way I did it. Now does anybody know how to get the door card back on?
