I change them when they seem to need it. Upon purchase I changed them, and I haven't done the 300D since. The 240 spent some time sitting without a fuel cap (still not sure how that happened), and I changed filters afterward. It still hiccups once in a while, so I may need to do the filters again. I probably should clean the tank strainer too, but I'm a little lacking in places to do that.

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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.