Assuming it's a 2 stroke......What kind of 'dust', if it is silver then it's metal. If it's metal then you need to do something about it. Find out if it is steel or aluminium using a magnet. If it's steel then it's more serious and will mean a complete tear down (top and bottom), if it's aluminium then get the clutch out and look at the plates for damage and wear, if they are worn they get hot 'cos they slip, when they get hot they get weak and can break into bits, ending up getting mached in the tranny.
If you only have a little amount of alu dust in the oil it could be normal wear from around the clutch basket/plate contact areas. It sounds like you need to do oil changes more often though.
If the repair of the impeller seals went well, and you used plently of oil on the seal lips to avoid snagging them, then it is still possible you have water entering via the tranny overflow during power washing(plug it up next time to be sure) or riding through streams.
I agree with Hunter, whiteish oil (emulsified) means you have water in there and need to fix.