I have read somewhere about oil on the driver's floor mat. I think I read that something about the oil pressure gauge leaks eventually. Could someone get me started in the right direction?

Thanks,
Doug V.

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1980 Mercedes 300 SD, 215,000miles
2001 F-350 Powerstroke turbodiesel, Crewcab, 4x4, 81,000 miles
1993 Chevy Suburban, 185,000 miles