So I’ve been away fighting wildfires so haven’t had time to do it. But just purchased a rebuild kit for both back calipers. Last time I bled the brakes there was only air bubbles coming out of the one back left caliper and it formed up again.
I have a 78 C3 had the brake lines changed last year and brakes worked fine. Then randomly had spongy brakes so I replaced the master cylinder bench bleed it properly and bleed the whole system afterwards. Had no issues for 20 Kmart form brakes then went spongy again. (No leaks anywhere ether)...