So I decided to pull out the aerial base and make a new gasket, how hard can it be right?
So out came the base, gasket made and base reinserted. All plugged in and the threads on the bolt / nut crossed so the whole lot was taken out again.
Reverted to plan A. Aerial base stripped, amplifier removed and recommissioned, holes plated and welded and awaiting filler. Washer jet pipe extended, fed through the boot lid and awaiting a new washer jet.
Now awaiting filler and paint on the roof and a new washer jet, not sure what to do on the latter as I could re-use the tiny one from the aerial base, use an old one from the front or buy a new one ...