I replaced both at the same time. I couldn't tell you if it "needed" to be changed out or not since I do not have the equipment to measure signal loss, but since I was upgrading the in-mast cable to much lower loss LMR-400-UF cable it just seemed counterproductive to leave the very high loss RG-58 cable in place. I was running an NMEA 2000 backbone cable from the main mast to the nav station and new radar cable from the Mizzen to the nav station at the same time so I had the whole thing opened up anyway. Actually still have it all opened up.
