you are useing a correct flare nut wrench?
[ the kind with the extra bits on the sides ]
the part is all one piece clutch master to slave and is a bwitch to get in
and costs about $150
bleed out the old fluid, do the brakes too at the same time
old fluid traps water and that causes RUST
but I see no need to replace a nonleaking line
worst case if you break the line or muck up the nut
buy or rent a flaring tool and union to splice on a short bit of new line
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Question wonder and be wierd
are you kind?