Pete, putting "something" inbetween won't really work.
My guess is that the o-rings have expanded over time and are now too wide for the nudges they slide in. That way the friction on the brake wall will be so great that the o-ring can hardly open up and accually brake on the wheel rim. My suggestion: excange the o-rings for new ones. They should be about 0,15mm thicker than the actual "nudge".
Brakes are a somewhat tricky and sensitive matter, especially the o-ring type. I'm currently working out a new "concept" which will be running with rubber brakepads, and am also having my share of "problems"....
Regards
Hank