Is it possible you are sucking in air thru the hose that connects the brake master cylinder reservoir to the clutch master cylinder? My 307d was low on hydraulic fluid once and took a gulp of air when I went around a corner. The system is designed so that low fluid causes the clutch to fail before the brakes, at least it was on my 307d.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13