I've owned my '94 850 (auto, 108k miles) for four months now and am convinced I'll probably be a customer or life. My ONLY complaint is about an intermittent-but strong- sulfur smell I get with the windows down, as I roll to a stop (never with the air on and windows closed). Two mechanics tell me it's a smell from the catalytic converter and can be cured using a "catalytic converter cleaner"-which none of them or parts stores seem to have, but everyone seems to think exists. "Snake Oil!" said my Volvo dealer. "It's a common problem in Volvos and Saabs. Up your fuel grade to premium and it'll go away." Three tank-fulls later it still stinks. Another mechanic friend recommended replacing the gas cap. " It's probably clogged and building up pressure and backing up into the converter". I give...any thoughts or suggestions?