Be careful about committing yourself to new flex lines. They aren't rubber except for the outer sheath which protects the nylon line inside.

Depending on how rusty things get where you live, you could be in for a real project if you just decide to replace the flex lines. In other words, loosen the hard line at the caliper first, where it is easy to do, to see if you can then get fluid to bleed more readily. The clog is often just in the bleeder passage in the caliper.
--
Art Benstein near Baltimore

A group of chess enthusiasts checked into a hotel and were standing in the lobby discussing their recent tournament victories. After about an hour, the manager came out of the office and asked them to disperse "But why," they asked, as they moved off. "Because", he said, "I can't stand chess-nuts boasting in an open foyer."