Replacing both the 2 and 5 rec used to be common practice. Not long after EV 100 systems came out there was a problem with parts. I worked for Clark then and we were told to replace both as a precaution. I think the part manufacturing problem has been rectified by now. Crown has had a problem with 3 recs made in India. They have changed manufactures. I don't think it is necessary to replace both recs unless they show weakness when tested.