That's an o-ring, it and the other seals can't survive the temperature of the powder coat process. You need to gently work that out with a scribe or dental pick. Be careful not to damage it. It is just sitting in the groove, but it can be surprisingly resistant to coming out.
Whomever you have doing the coating should be familiar with coating jet pumps. Coating, or more importantly, sand blasting the mating surfaces will destroy the alignment and fitment when you reassemble. The most critical is the register and mating surfaces between the bowl and suction housing. If this area is blasted and/or coated, the pump shaft could bind. Other areas of concern are the pin bores in the diverter and all threaded holes.
You will have to spend a bit of time, before reassembly, cleaning off excess powder coat even if the parts have been masked carefully.
I emphasize caution because I have seen numerous pumps destroyed by blasting the machined surfaces. Legend pumps are not easy to find parts for.
