E30 door lock problem

[John Smith <john@xxxxxxxxxxxxxxxx>]

The drivers side door lock on my '89 E30 325i (2 door) is
working its
way toward total failure. When I turn the key clockwise to the
horizontal
position the other door and the trunk/boot locks just fine.
However the
push-down button inside the car door does not always go down and
the
door remains unlocked.  Sometimes the button will go down a few
seconds
later. The door always opens (unlocks) without problems.

The actual barrel of the lock feels really rough as I slide the
key in (and out).
I tried wd40 on the lock and what I can see of the internal
mechanism but
that hasn't improved anything.

Dismantling the entire mechanism looks like a big job from
what I can see throught the door panel and I can imagine myself
with a
heap of parts like the inside of a watch and not  figure out how
it goes
back together again :-)

I was wondering if it practical to exchange the drivers side
lock barrel
with the passengers side drivers side (which is infrequently
used) or maybe
better still the trunk barrel? (Presuming I'd have to buy 3 new
locks otherwise?)

Anyone had this fun experience before? TIA for any help.

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