at the side of main pump on a elite 30,servowarm ?

main pump unit on elite 30 has two out lets either side of the main pump, valves inlet on left &outlet on the right;i suspect that they both have "seals" in them? BUT,outlet valve is dripping out & when ive look under it needs correct tool to be used ;too under the valve so too replace the seal
valve unit? iwont do this while its in operation or while the system is full . what can you recommend,and where do i get spares from please, if possiable .