There are rubber O-rings in there too.

(See your Bosch service station and replace with "VITON")

If the FSM torquing procedure is not followed exactly the copper rings will leak.

It is possible to "WARP" the I.P. under undue stress (I.E. "Torquing" incorrectly)

I would only use the delivery valve(s) specified by either Bosch or Mercedes.