Great tip about the conductive rubber degrading over time. The 6mm loop on my favourite electrode failed to register on my DVM even on the 10M range. ,Being both a cheapscate and lacking stocks of spare rubber I found that rubbing the surface of the rubber with a green ScotchBright pad left it with a new conductive surface - perhaps not quite as good as new rubber but...
Anyway, it was like having the brake-pads on your car changed - all my bits flew forward at speed on first application
BTW - 32/0.2 wire stripped out, twisted and tinned at each end makes a really good flexible metal core for the rubber.