I have a similar problem on my '70 220 gasser. I've mentioned it on the forum, and another poster reported the same problem... but no solutions. Some kind of ghost... I'll flip the key and absolutely nothing though I have power, not a verifiable 12v (haven't yet tested it during one of these episodes), but enough for everything but the starter to behave normally. Placing the car in 4th (it's a manual) and pushing it back a foot or so is the only thing that reliably "solves" the problem. Otherwise, waiting or "shaking" the car as you said have worked in the past. My car's previous owner reported all this to me as well--he could never figure it out.

Panda, did this occur on your 220 also?