I have a diesel W126 chassis car so the water pump experience I have is
not, I think, applicable. I've never heard it's too much of a problem though.

The central locks. Ah yes, well, um, er. It's not hard but it's pretty
damn time consuming.

They're vacuum operated. There is a regulator for each door and usually
one of them fails. The regulators aren't teribly expensive and even cheaper,
George Murphey used to sell replacement diaphragms for $5 ea.

Step 1: get a mighty-vac (or equiov) vacuum tester. You can't do this
without one.

If memory serves (it's been a few years) the vacuum lines are under the carpet
on top of the steel floor. One is vacuum and one is return - I *think*. By
carefully testing - again, I *think* the yellow one, you can ascertain which
door vacuum reglator is leaking. Then you have to pull the door panel off (easy)
and replace that unit.

The trunk and fuel filler door is also in the circuit.

Get the service manual... it requires removing the distributor so timing is
an issue.