Thanks for the timely replys. In the vehicle's service record there were notes about using heavier weight oil up until the rebuilt the head. After that no mention. So I suspect the cat took the oil injestion and started its spiral towards death.
I won't ignore the possibility of it idling or running rich. As far as idle, there does not appear to be a lambda closed loop system. I am familiar with them as they exist in my 81 Volvo and 80 450. So I might have to make a trip to a mechanic and hookup an exhaust analyzer. As far as running rich, I'll check my plugs in a few thousand miles and see how they look.
Any other suggestions are welcome. Cheers.
S, J.R. Brown
1986 280GE LWB Anthracite
1980 450SEL Champange
1981 Volvo 240DL UPS Brown