Heater return tube

[LA48340]

Today I replaced the water pump on my 88 240. The new pump came with a gasket, an o-ring for the joint to the head and another small grommet gasket. The small grommet style ring I think is for the heater return hose compression joint. When I dis-assembled it, the end of the heater tube(metal) had a white plastic ring at the water pump joint end...thinking this was the seal I cut it off. It appears this ring is permanent and squeezes the grommet ring in the water pump cavity.
Does anyone know if this ring can be purchased as a service part. It leaks very badly without it.
thanks.