i have almost the same problem, I think it is high resistance in my right hand indicator circuit, because when there is no other load on the battery and the engine revs are high I get some flashing going on, but the second it drops to idle or more lights come on, the flash drops to error cond. But i do notice that when towing a trailer, on which i know the lights work, the right flasher on my car will allways work and will drive the trailer lights as good as new. Its been like that for years, but someday I plan to re-wire, Just not right now.
But yes i do beleive it to be caused by high resistance somewhere which sets off the flasher.
Sam