a hydraulics technician once told me that whenever a copper washer is being used as the seal, first make sure its really soft (anneal it if not) and when tightening it before coming up to final torque - about 10% short loosen and tighten the bolt/nut about 5 times, then finally torque it down.

I also follow this on the oil sump washer and the ATF pan washer too. It doesnt even seep.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)