Sounds like a fluid leaking onto a hot spot as previously mentioned. Just make sure you don't have a seized brake caliper as that can get quite dangerous. If one of your front wheels is significantly hotter than the other after a bit of a drive, that's a clue. If so, get it checked immediately. Seized calipers can cause a nasty fire.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition