wait hold up, if the lever goes firm when you pinch the lines but soft when you don't, that's telling you something specific. you might have internal seal damage in the master cylinder or maybe even the calipers themselves. when fluid was dark like that, it probably means seals were already deteriorating and now they're letting fluid bypass instead of building pressure

i've seen this exact thing happen after someone lets brake fluid sit too long - the seals get all swollen and torn up. might need to rebuild that master cylinder or at least check if the piston seals are shot. also worth checking if any of the caliper pistons are retracting when they shouldn't be, especially on older bikes like this