I agree it sounds like the starter. Since they are rather expensive for these cars, you might want to pull the starter and get a local parts house to do a bench test on it. They will usually do it for free.

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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 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.