We have seen similar service of this application on moyno pumps as well as rotary lobe pumps, the system was a split mechanical seal. The split seal worked very well with a rifled bushing in the stuffing box that removed the high solids and allowed the seal faces to flex with the high product...
Greetings, there is a company in Florida that sells by the ea. the split o rings, the size you are looking for is listed as a (dash) - 42 o-ring. you can contact them at 863-425-9611 to help
