On Friday, June 22, 2018 at 6:22:58 AM UTC-7, wrote:
No whatever banana I stick in there is intermittent.
(I use a lot of BNC to dual banana plug adapters.. then I can watch
the fast stuff on the 'scope at the same time.)

GH

Banana jacks are so simple that, in the absence of obvious physical abuse, I find it hard to believe that it is intermittently faulty. I would try soldering test leads directly to the lugs; when that does not fix the problem, I would look somewhere downstream like a crack in a pc board or a cold solder joint.