250-500cc quick question wr250

come on guys,need little help here.......on the waterpump shaft theres a spacer that goes inside the seal ring in which theres a oring,i cant remember if oring sits against the impeller or the other way towards the casing,also do these spacer parts wear down?im going to order one tomoz anyway,as ive changed bearings, seal ring n oring but it still leaks into coolant,which is why i think i put the spacer in (n oring)wrong way round,any help appreciated,cheers.