Volvo Repair: (91) 740 Wagon, oil filler cap, flame trap

Question
Dear Sir, my daughter has a 1991 740 wagon that uses about 2-3 qts. of oil a week. She just brought it to me this weekend.  There is a lot of oil on top of the engin (fresh looking) and the oil filler cap seems to build up presur and leak?
There is also oil on the inside of the hood, like it is being slung upwards?  Off the top of my head I would say it was the rear main seal, but what do I know.  I was told it would build psi. and leak if another oil filter (other then volvo) was used?
Is there any problems that you may know off to help.
Thanx,
Luke  

Answer
I would replace the oil cap seal.and replace the flame trap.the flame trap box is under the intake manifold.the flame trap will be inside of a plastic housing which is located between intake manifold runners for cylinders 3 and 4.it will have to hoses going to it a large one and a vacuum line.inside this plastic piece is the flme trap