Hello Allthunbs .
I've bitten the bullet and fitted a new speed control , at £81-00 GBP ! Ouch! Just for the part (I fitted it) . Relatively straight forward soldering and insulating job . There are some people advocating direct wiring , bypassing the control , but that does away with the soft start , which I like . My old 4 horse Ryobi didn't have it and that was a pig when it kicked in ! There does seem to be a quite a few people out there with the same thing going on though . I think it will be back to Makita after this !