Hi

I had exactly the same trouble with my locks.  I bought a replacement from a
breakers yard after discovering the solenoid unit in the door affected was
malfunctioning.  It was £20 for the replacement, though this will vary and
could possibly be haggled over.  It was 20 minutes to fit, so if you have a
friendly mechanic, ask him/her, or have a go yourself and expect about an
hour.  It has worked perfectly since.  Getting the door panel off is a piece
of cake the second time, working it out the first time is a bit of a pain in
the aris.

The duff unit was knackered, so I doubt it would be possible to fiddle with,
but as I have never tinkered with this type of equipment before, I don't
know if they can be repaired.  I doubt it and suspect the law of diminishing
returns applies.

Good luck

Strange lad
--
I can speak Esperanto like a native.
Spike Milligan