Using synthetic engine oil helps keep the sludge at bay. AutoRx and Seafoam are not 'additives' but treatments and are not to be left in engines for 3-5,000 miles, waiting for the next oil change.
One of the benefits to changing the oil separator box, is changing the vacuum lines that are part of the system. After 10 years, the lines get brittle and start to crack, which causes leaks, which then causes the engine to run rich, which then causes the O2 sensors to fail.
Ask your dealer if the mechanics ever clean out the PCT nipple. I'll bet the answer is no. More income is produced by replacing parts than 'fixing' the problem.
Klaus
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Proud owner of a 220S. If I had more room, I would have more Volvos.
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