I've started asking callers about the maintenance of their efm stoker/boilers. Many are replacing the domestic water coil, burner plates or burner worm and pipe for the first time, after 25-30 years of use.
This also agrees with our parts sales.
The best thing you can do is to keep the stoker mechanisms lubed, use the clean-out lever when you check the ash can, and clean the inside of the boiler, flue pipes, chimney base, including the holes in the burner plates, in the Spring. Also, check the tightness of the coil nuts every season and fix any water leaks immediately.
If I was going to carry any spare parts, I would have some burner plates and a burner worm and pipe. The bad news is that you may never need them.