Does anyone know if these ever fail / play up?

I was wondering if that might be part of the problems I seem to have with my turbo - a lack of vacuum to move the vanes. Also somedays the brakes seem to feel effective than others, and then it hit me (well not literally!) this morning when I was driving into work - these are both vacuum driven.

Any thoughts?

Usually lack of vacuum is a leak. Check pipes and joints for splits/breakages. Common on other (older) VAG TDi cars. Brake servos are also known to leak.

Vane actuator is also prone to sticking with age, it is possible to lubricate/work the shaft to free it up.

Where is the pump on a 110TDi - I don't recall ever seeing it, but that said I have never specifically looked for it. Maybe I'll consult my Haynes book of fibberations later.