I've been busy and have had the tools lined up for this job for weeks. The thread was so badly stripped I didn't need to drill it out, I just used the tap straight away with plenty of oil. Then I wound the helicoil in, broke (and found!) the tang, flushed it through with some petrol while turning the main shaft, and left it on a wheel ramp with some fresh gear oil inside. I used a 9/16" x 12 UNC helicoil kit.
No leaks yet.. but if it does leak, and too badly to live with at that, I think I'm more likely to put a new "Roamerdrive" on than try to source a good Fairey casing and rebuild this one into it. Fingers crossed. If the tray is still dry when I'm next in the garage I'll be putting it back on with some anti-scuff paste and a new gasket and the floor and seat box and seats will follow shortly after!
