Chaps, by way of an update, and again, thanks. Have done 400 successful miles in the old beast since I last posted and although I cannot spend too much time looking at the wobble for obvious reasons (!), it seems to dissapear when car is hot, and has been for a while. I've now taken a look at all the hoses.
The one I assume goes directly to the gauge - as it dissapears into the bulkhead on the drivers side - is original, judging by the amount of grime on its small white sticker and the zip tie looks ancient. It's in good condition. What I did find was that the clear hose that comes off the breather nipple is not attached to anything. So it looks like it should go between the two large pipes beneath the turbo (attachment) so I have attached it and fired it up and after some initial wobble when idling it calmed down and was still (or almost still, the kind of wobble one would never spot unless looking).
I am a true novice on cars, does this sound right?!
Just spotted Carrera's post - will give that a go ASAP.