There are two possibilities for those white 'maggots'.
Firstly that they were in fact blowfly maggots, laid in the droppings and hatched out since - but you seem to clear up more quickly than that, the droppings would have to be quite old for that (how fast maggots hatch would depend on temperature)?
I think they were probably tapeworm segments. Paramectin doesn't worm against tapeworms, so you might want to drench them with something that does, like Albenil or Ovispec. I've only seen the white bits once, in the droppings from a tup lamb I'd just bought. Mostly we worm against roundworms since they're the big problem but obviously tapeworms turn up sometimes.
Is that what's making your lamb scour - probably not. But if you wormed everyone with something that got tapeworms as well as roundworms, you'd cover that possibility anyway.