AU3 Fairmont: Hissing sound from climate control display

[rowan194]

There is a vaccuum tube behind a small vent at the top left of the clock. Today it started audibly hissing, the level changing with engine load.

With the message display centre removed I can put my fingertip on the tube and it will stick within a couple of seconds so it has decent suction. Maybe TOO much suction, like there's a vac pipe blocked somewhere else?

Since the hissing started this has also happened:

- Twice the transmission held first longer than normal, and when it did change to second it was quite hard.
- Once the trans/diff did a 'clunk' when pulling up to a stop.

But apart from that:

- Engine is idling fine. No surging, no stalling, no RPM wandering aimlessly.
- Power and response seems to be normal.
- No obvious vac leaks within the engine bay.
- Transmission only played up the 3 times out of a couple of hundred gear changes. Could be coincidence.

Any ideas why this tube has suddenly started making some noise? (Note it is actually a tube inside the MDC, nothing to do with the climate control actuators further inside the dash)