Looking at the way the crank has gone,i doubt that there would be that much swarf/bits of metal anyway-You have the gauze filter and the oil filter to protect the engine,so i wouldn't worry about it too much.I would agree with Rob,highly unlikely to be oil form the rear cylinder,more likely from the breather.My SP5 used to get a fair old pool laying at the back of the rear pot until i put an STM breather on.