Volvo Repair: oil in air filter-smoking, flame trap, volvo 940

Question
Some time ago my volvo 940 suddenly started to let out great clouds of smoke and for a second it lost power. Then all was well again for a while then it happened again. I took it to a local garage where they said it was the breather pipes blocked. I replaced the air filter as it was covered in oil as well as the plugs. I also flushed out the breather pipes and replaced the flame trap.
Great for almost six months now it has happened again. The air filter is soaked in oil as well as the filter box having a large amount of oil in the bottom of it. The breather pipes seem to be clear this time but it just keeps letting out great puffs of smoke and loosing power. and then its ok for a while.It would appear that some how oil is getting into the air filter somehow.  Please could you advise is it ready for the scrap yard or can it be saved.
              Yours  sincearly  Mr D Kendall

VOLVO 940 ESTATE HIGHLANDER Reg 1993
1986cc petrol

Answer
The only place that oil could get in the intake is either through the intake opening, or from a faulty turbo.  The turbo would dump all of the oil in the intercooler though.  Its a tough one to say where its actually coming from.  It could really only be found with a visual inspection.  Look all over the engine compartment for oil or a greasy dirty build up.  Where ever it stops is where its coming from.  It has to be coming from somewhere if its getting into the filter.  Once you find the problem then you can evaluate whether its worth the money/time/effort.  This is the first time I've heard of a problem like this so I don't have any past experience to draw from for any other reccomendations, sorry.  

James