Hi Andy,
Thanks for reply.
Quick version!
Bought the car (2001 2.5tdi) and had the front passenger side replaced after about 4 months as was constantly down and proved to be leaking.
As I was working abroad for that four months - didn't know about it until I came back, so as a result compressor been working like buggery trying to pump up a leaky bag.

When bag was replaced, car was fine on two lights, no leaks and stays up.
However when it drops to one light, it struggles to pump up to two, and warning light comes on in the dash.

Rarely gets to three lights.

No real loud noise from the compressor unit, purrs away quite nicely.

Hope this helps

Mark