I took the engine shroud off this weekend.

The oil was not coming out from the head gasket (good) nor from any
other part of the engine itself. (good)

The oil was coming out of the air cleaner box, part of that box has a
tube to the crankcase and also an opening to the fan blower. This part
of the air cleaner box is a separate compartment from the intake air
filter. I guess the idea is the fan provides a positive pressure for
crankcase ventilation. Apparently there was an accumulation of oil in
this part of the air cleaner box and when I made a sharp turn, some of
it spilled out onto the muffler. I'm not sure why there was a large
accumulation of oil there but I cleaned it all out and all seems to be
well now.

I should have mentioned earlier, this is a Tecumseh engine on a Sears
riding mower.

thanks
Mark