I have an 89 740T, 165K miles, and I have oil leaks around the oil filler cap and teh front seal. I cleaned the plastic Y- fitting on the breather hose checked the flame trap for blockage by removing the filler cap and blowing through the hose into the crankcase. There was a minute amount of resistance, abut what I would expect from blowing through a comparable size hose. And not very tasty, either.
I checked the small black intake manifold anti reverse pressure valve (sorry- I don't know its real name), the one located more or less behind the alternator, and it only works one way as it should. But I also checked a red and white vlave that is on the intake manifold to waste gate line, and it passes pressure both ways, with about 50% restance in one direction. Another problem that could be related is my A/C system shuts off under boost and passes heat- I can hear the flaps close.

Could this be the source of my problem?
If not, is there something else I should look for?
Is the Volvo dealer the only source for this red and white valve?

thanks on advance

Rick