Originally Posted by Beagle

D-valve seal rings on 123 series MW pumps are made from a 0.50mm precision annealed copper shim and may only be used once. The correct size is 14Ø x 10 x 0.50mm only available from a Bosch agency. Only by using the correct part will the lapped faces between the D-valve and pipe connection be kept parralel to seal at 40-50nm in a single step. Overtightening can distort the pump body and cause rack to stick. NEVER re-use or use a substitute.