Hi there,

You have to change the 0-ring AND the reservoir. Re-fill the reservoir, lift up the front wheels, and turn the steering wheel all the way left and right about 30 times before starting the engine. Then re-fill to proper level.

There are several detailed procedures written up. You can search for it.

Your pump should be OK.

Hope this help.

Rene

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'99 ML320, '00 C280