There can be quite a bit of oil in the intake from your
turbo. When you take off the hose that goes over the
engine you will see it all along the edges. It can collect
in the intercooler which has a hole in the bottom where the
oil blows out. If you don't have blue smoke out the back
of the car I would not be concerned.

As far as the fuel injection ecu, I guess there must be a
fault code that indicates a problem. I'd have the fault
codes reset and see if it re-appears before considering
replacement (as long as you are not seeing any associated
problems).

The O2 sensors problems can be triggered by wiring problem
(I believe). Might be valid to check the wiring connections
and clean them up, first. The Bay 13 site (http://volvospeed.com/Repair/o2sensor1.htm) also says replace
only if you get the codes more then once after resetting.