Right, had the oil cap off, one breather pipe (narrow bore, with a pretty tiny hole in the oil filler cap to let air through) goes to the inlet side of the engine, the other (wider bore, big hole in filler cap) goes to the airbox. Neither appears to be blocked (blew down it, not sure that's good for you) and the cap isn't blocked either. Reckon I'm going to try a new cap tomorrow as you cant' replace the O-ring on it and they're apparently meant to be swapped every 60k...