I always just replaced them.
but we had to charge $100/hr for labor too, so one hour's labor for rebuilding the plate assembly is $100...plus the o-rings plus the labor to remove/reinstall (with the engine on the bench no big deal but in some equipment it is a real pain to deal with in the frame). So by time you paid the labor to rebuild + R&R of the assembly + o-rings and gasket, they were at about the same cost to replace it as an assembly. Then if there was a problem with it (sticking?) rather than the shop have to eat the labor, if we replaced it as an assembly we'd then file a parts warranty which kubota paid labor on. Pass the liability onto the manufacturer so to speak.
I think there was one guy who wanted his rebuilt, even after we gave him the option to replace the assembly at the exact same dollar amount. I think it was an old ZD18 as I remember. Fine, we rebuilt it. He picks it up, and gripes about how much it cost to replace and o-ring and seal. Well sir, I hate to tell ya, but I told ya so. Enjoy your mower. Few years later it shows up won't start. Cranks fine. Other tech found fuel plate stuck. He took it apart, freed it all up, and reassembled. Far as I know it's still going....but I dont' work there no more so who knows. I did find out today that the customer in question passed away this morning.