Now I feel stupid! This is a sticker-foot that seems to have migrated from the bottom of the case somehow as pointed out by a friend from RadioReference.
Over the years the other 3 have apparently disappeared and somehow that one appears to have migrated to the rear case. The box has been vecro-mounted in my radio cabinets for most of it's life and I took it out and handled it for the first time in years this week. It just sits there and decodes faithfully day in and day out.
It looked just like an LED in one of those little plastic sleeves the I use for other purposes. I had tried to peel it before but, being afraid of ESD, I did not try too hard. It was stuck on there pretty good. When I pressed it it seemed to move in slightly so I was thinking reset button or some sort of LED in a sleeve.
I will be sitting back here in the corner, don't mind me.
