Mine would never stop leaking until I stopped using a screwdriver to tighten the clamps and went with a socket and driver. It's a pretty large hose to seal with a screw clamp, and so you have to apply more force to the screw to get the same sealing pressure per inch.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles