not disc caps! they are metal oxide variable resistors. they look just
like caps. keep the shell and replace the mov's. it will be good as new.
buy extras because the mov's can only take so many hits (or just one big
one) before they are ruined. if you arent satisfied with the performance
of the cheaper surge suppressors then look into a transformer based one.
i have two ONAC brand line conditioners. they are more expensive but
they never wear out. (excluding direct lightning hits of course) i got
them surplus at a junk shop that salvaged computer equipment. its been
more than ten years with out power line damage with my set up. i dont
have $40 in both of them but i got lucky. when bought new they are not
cheap.