if ur left front caliper is making noise like a hissing it is more likely the piston in the caliper is leaking or the seal around it is. but you said now the pedal isnt going to the floor so that doesnt add up either??? as far as the bleeding sequence,you may be right but i always start with the caliper farthest away from the master cylinder then work my way back as i stated earlier.but do what makes you happy man. i would def replace the bleeder screws tho they are like 10 cents v.s. the caliper if ur not getting any fluid out the bleeder then there is a blockage somewherein order to clear it completely remove the bleeder screw to allow the blockage to come out while pumping either brake fluid through the lines or if you wanna get em really clean you can go with like kerosene but just make sure you re-bleed with good fluid extra good if you do a full break line flush! and i hope you understand all other bleeder valves will have to be closed while you are flushing the one that isnt flowing and that one has to be COMPLETELY REMOVED! hope this helps.