Derek thanks for the Maplin tip. I've now had the chance to do this - I replaced both male and female plugs (the Maplin connectors are great - a grub screw securely holds the centre wire) and reception was much improved while I had the aerial free. When I fitted the aerial back into the wing however, it dropped right out again.
After much jiggling and checking of contacts I found that the cables were now so taut that I guess there was tension somewhere making the original aerial useless (though after one refit it was not bad). I did my best to sand the underside of the wing but I can only just get a couple of fingers just into the recess.
I got a cheap removable aerial from Maplin too (the same is available at Halfords) - the only one I could find with very little bulk below the wing (it's very cramped in there) and an angle adjustment that was suitable (the wing is sloped), and once connected to my new, regular-sized connector all was well.
Unfortunately, the new aerial requires a 10mm hole, but the MG hole is 22mm so I had to fashion a strip of metal under the wing to hold it down and the rubber seal above only just covers the hole but so far so good!
Thanks for your help.
