Hi Dean,
I went to Jack Walker today - I've been losing sat nav intermittently so took it into them on your advice.
They ran a VAGCOM diagnostic and found no error codes from the aerial, GPS, or otherwise. The system was all clear.
On the way home from work, satellite signal varied from 0 to 5. Normally I have between 7 and 9. As of now it's reading 0 again!
I also had them check out the AM reception, which has totally deserted me, and they couldn't find anything obvious (FM is a bit dicey too, but not as bad). They're recommending a new antenna. I've tried a halfords replacement aerial, but apparently the GPS system needs a specific bee-sting aerial so it might be a problem with that, although it's nothing obvious.
I mentioned the water in tailgate previously, and I explained that I thought the antenna booster was within the tailgate somewhere. Do you know if this is the case? It's possible that there's a bad earth in there.
For me, the fact that the GPS signal is coming and going would suggest a bad contact, bad earth or something along those lines, rather than some major issue with the system itself.
One minor gripe I had was that they managed to scratch the corner of the RNS head unit when they were removing it - not good. A blemish on an otherwise unblemished car!
Any suggestions?
Cheers,
AndyC