Use the hydraulic jack with a 2x4 piece of wood on it. Raise the jack underneath the oil pan until it touches securely. Remove the bolts holding the engine mount on. Raise the jack until you can remove/replace the engine mount. Lower the engine and install/tighten the bolts holding the mount then move to the other side. I have done it on my 300D but not a 240D but there should not be any difference. I personally do not think it is going to resolve your hard start problem though.

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Jim