So I did update this on another thread but
@jl1 here you are - I went to Leixlip tyres, they filled with new gas and it made no difference so they removed the gas and left the system empty.
I called VW for the part and it was €85 for just the sensor so I picked one up off aliexpress for maybe €6. Yes it takes a month to deliver but it's a big saving.
I'll then go to VW parts to get the O-Ring which I have the part number for.
I'll fit the lot in a month and go back to Leixlip tyres where they'll fill with gas again for around €50.
@jl1 you need to know for sure it's that sensor through VCDS and not one of the more likely other failures!