Rear Brake Pad not Clamping/braking

[BadAss95-530i]

Ive noticed some very slight rust buildup on my rear drivers side rotor (which I take to mean that the pad isnt making contact). A local indie told me a brake fluid flush would take care of it and get it kicking again.

Im assuming when my clutch was replaced only 10 mos ago my fluid was flushed. Has anyone had this problem or know the fix? Or is another flush truly the answer?
Thanks

(Rotor and pad both showing age/wear, but have plenty of life on par with the other 3 rotors/pads which work fine)

[Ferret]

Ive noticed some very slight rust buildup on my rear drivers side rotor (which I take to mean that the pad isnt making contact). A local indie told me a brake fluid flush would take care of it and get it kicking again.

Im assuming when my clutch was replaced only 10 mos ago my fluid was flushed. Has anyone had this problem or know the fix? Or is another flush truly the answer?
Thanks

(Rotor and pad both showing age/wear, but have plenty of life on par with the other 3 rotors/pads which work fine)

A 'flush' wont make a difference here, a bleed maybe, caliper dismantle? definitely. Pull the guide pins out of the caliper and see if they're sticking at all, then bleed em up...

[Ross]

Ferret is right.
A brake fluid flush will coincedentally bleed as well but unless you also have low pedal this won't be your issue.
A more likely cause is that the caliper has rusted in place on the pins and not sliding, if the rust only remains on one side of the rotor that is a sure sign of this.
There is also the possibility of deep pitting from a prior period of inactivity that has yet to worn away, but as above if it's only on one side look for a stuck caliper mounting and probably one pad worn far beyond the other.