Checked it out today
Ruled out the brake line itself as the problem.
So I pulled the caliper and disassembled it. Found rust to be the culprit. Pistons are in good shape (no pits) housing has some pits but should be ok. The dust seals were both still in fair shape not split or stiff. I guess they just didn't seal properly.
I checked the rotor with a dial indicator for warp. Barely had .02 mm runout.
So maybe I'm lucky. Looks like all I need is a caliper rebuild kit.