I've been told by the last mechanic to work on the car that it's an internal problem...one dead piston, basically(?),so it's blowing out oil---approx. 2-3 quarts/week. He pulled the dipstick out about a 1/2 inch so that some of the pressure could be released there instead of through the filler cap so there wouldn't be so much stink, smoke, and burn.
He first tried changing the seals, but after doing so found pressure continuing to build.