Just an update from yesterday as I was up the mast.
I took the SDR tube off and removed the contents - it was all totally dry inside, no signs of damage to the amalg tape I had put on it a few years ago, all the connectors were pristine as I had amalged everything thoroughly.
I got the lot home and ripped the SDR apart. There was no signs of any moisture or wet inside although I observed strangely some oily type of residue substance where the PCB met the case. The blue squishy thermal foam was dry. The heatsink thats stuck to the bottom of the pcb and mates with the case was not fully stuck, but it looked to me like the glue used on its sticky pad was the source of this substance.
It certainly was not water as I gave it a blast with the soldering iron inside the metal case and nothing evaporated with considerable heating of the case.
The residue, seen along a line where the PCB met the case sides:
The Squishy blue stickon thermal foam removed from the component side and here the underside, where the heatsink was stuck on - identical residue where the pad was "stuck"
The heatsink sticky pad
Im confident there was no water ingress and the residue I am seeing is from the glue thats used on the pad to stick the heatsink on.
Anyway.....
I cleaned it up, replaced everything as should be inside the case and ran it up on a spare Pi with a little aerial attached. it worked fine.
So - conclusion is that it was the USB extender that had karked it, up the mast. I can not test that as I cut it off to save me time on site.
Ive spoken to keith and I have some cable, adapters and SDRs on the way to get the unit back up and running. I think having the SDR inside rather than up a mast is the best way to go.