When I pulled the housing from my water pump to replace the impeller I had to remove this stainless ring with a plastic insert before I could remove the impeller off the drive shaft. I mangled the stainless/plastic piece as it would not come off easy. There also where some shims under the stainless/plastic ring and do not see any of these items listed in the water pump or lower unit break down of parts. Where do these parts show in the break down or are they suppose to be part of the plastic housing?