Thank you to all posters on this topic. I found by chance that my front passenger lock actuator wasn't working one afternoon. I forgot to lock it manually after fiddling and that very night the car was broken into. Fortunately not a lot was taken. I had to fix it as I can't bear to see my girlfriend standing in the rain while I manually unlock her door
My tips:
1. Use an impact driver to get the three screws out of the lock assembly - easy peasy.
2. Take out the electrical plug (push the tab DOWN) and the outer door handle connecting rod. Push the cap back over the outer door handle connecting rod socket. The lock unit can then be turned and moved out past the window glass channel....just.
3. Use a narrow blade chisel (5mm) to crack open the motor and cog casing assembly.
4. Drill down the channel in the plastic above the motor casing tabs with a 4mm drill bit and let it drill into the plastic beside the tab a little. This allows a stronger screwdriver to get in behind the tab.
5. The tab metal is tough. I broke off the tab on one side, and then managed to get the plastic top off the motor by pulling it up and out from under the other tab.
6. My motor had grease etc inside, as others have described, but the real issue was that the carbon brush on one side had completely worn down. It only went fitfully after cleaning and reassembly. A new motor and a spare are on the way from mopselectric on eBay.
7. There is a dimple in one side of the casing that is almost designed to be a screw thread. I nipped the top off this, drilled a hole opposite it in the other side of the casing and screwed a screw through the hole and into the dimple to hold the casing together.
$23 fix compared with $350+ from dealer....thanks everyone!