It sounds like the return spring. I occasionally have the same problem with my car sometimes, although I only have to push the pedal up about a centimeter or two. It doesn't really seem like a big deal, I just have to bump the pedal with my foot if the light stays on.
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K