Rear door lock and handle - help!

Hi,

I've spent a very frustrating few hours this morning trying to fix a problem with the rear door lock.

For ages now the lock has been unreliable, sometimes opening and sometimes not with the central locking. Sometimes if it doesn't open you can unlock it by pulling the interior handle, and sometimes this doesn't work either and the deadlock remains engaged. There is also a loud crunching sound comes from the lock on the occasions when it doesn't open - so it's obviously receiving a signal from somewhere.

Lately it has been getting steadily worse, unlocking probably one time out of 5. I read around the forums a bit, and a lot of posts seemed to point to an internal problem with the lock (dry joints, broken plastic, broken microswitch etc). I got hold of a second hand lock from Skospares (which was pretty cheap - less than