I like your subtle comment. The symptom was loss of brakes as I pulled into my driveway. I had to press real hard on the brakes and the azalea bushes did the rest. To diagnose the problem, I followed the FAQ suggestions of pressing numerous times the brake pedal (10 or so) then started the car to observe the action of the brake pedal. I got the expected drop of about 1/2 or so. Though I did hear some whooshing sound when the brake was applied, I wasn't convinced 100% that the brake booster had failed. I removed the check valve to check for a vacuum. Surprised that I felt nothing, I replaced the check valve with a valve obtained from a PNP donor. I got an audible vacuum. Further my original hose showed checking on the exterior surface. That hose is now replaced and the "new" check valve is in place. After a test run in the neighborhood, keeping my eyes open for azalea bushes of opportunity, the brakes seemed to be back to normal. My conclusion is that the original check valve on this 240Kmi car had stuck causing the brake failure. I further believe that the check valve, white or black in color, donated from 240/700/900's are interchangeable though I have no specific data.

For the fun of Volvos,
Mike
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'92 245DL, '90 760 GLT