Did an Audi Avant central locking pump. The interior was made totally of
graphite, which predictably had shattered. Can't remember if it was 300
sheets for the pump plus 90 for reprogramming, or 400 sheets plus 90 from
Audi agent. Can't see the logic of a pump failure if one lock still opens?
You can test for leaks by disconnecting from the pump and blowing down the
lines. You can detect if you just charge the lines and then no more goes in,
if you have to keep replacing the air from your mouth it's detectable and
you have an air leak. I could almost generate sufficient pressure using my
lungs to operate the doorlocks and could actually operate the fuel flap lock
by this means.

I repaired the A4 with a pump from a scrapyard Audi 80, which could be
adapted to fit the Avant pump unit body and was more heavily constructed.
Using the old pump body meant using the old electronics also, so no need for
reprogramming, so no 90 sheets. Total cost of repair £10 into the scrapman's
greasy mitt. All the secondhand Avant pumps I found were all u/s for the
same reason mine was as well as being pricey. No "pattern" units were
available.

Details of the Audi 80 repair (if this is appropriate), is on one of the VAG
repair sites, though I can't remember which one - sorry!

From what I recall, there are about 5 microswitches in the doorlocks in a
Mk4 golf, silently festering in a moist climate. Not an ideal situation for
electrical contacts. Marvellous they work at all really.

Price of a doorlock was around 80 sheets at the time I enquired.

I ain't 'arf glad my plain vanilla Sdi diesel Mk4 is totally manumatic
locking!