Just because they are cracked does not mean they leak.

I've owned many that had significant cracks, and I've only had had one leak.

Wait 'till they leak, then replace with another used.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles