No-one is scratching their head.
The causes are well-known and extensively documented.
All aircraft CAN suffer from this problem, but some are more prone than others.
If your engines are using 1-3 quarts/day, they must be a little sick. Our 146s don't use anything like that much.
No, not heavy maintenance, simple inspections will do it.
No 146s have "catalytic converters".
The best test for contamination is to take a blood sample from an affected crewmember- sounds like the crew you were with might have had other "substances" in their blood than oil.
Very appropriate user name, BTW.