I am not aware of any issues with bleed air contamination affecting the Challenger 600, which also uses the ALF 502 engine used on some models of the BAE 146. You would think that if there's some design defect in the engine that allows oil into the bleed air, then this problem would have appeared on the Challenger 600 as well. (Most Challengers use the CF34 engine, a completely different design.)
I wonder if anyone has had a real close look at the Air Cycle Machine, since an ACM problem might cause contamination.