I'm leaning more toward bad master or low reservoir. My '77 had a bad slave cylinder when I bought it and it was fine in normal driving, just needed to add fluid and pump up about 50 strokes at the pedal after sitting overnight.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.