[murrayf]

contact tech support at rm you can call them they will help you

 

[murrayf]

its a spacer so no recess

 

[murrayf]

regular buna rubber orings will work (harbor freight kit)

i use permatex waterpump and thermostat silver rtv in the little tubes

like this''

Permatex Permatex? Water Pump Thermostat RTV Silicone Gasket 22071 | eBay

 

[murrayf]

its a spacer and if it was not there it would have ground the polo mint or graphite seal up and scored the back of the impeller on the rear cover

so it was there and has fallen prey to your personal black hole

good news to find the original simply buy and get a replacement the original will pop right up