I have an Australian model 83 S2 Rx7.

Whenever I turn right and brake I get a distinct metal on metal drone from the left rear brake. Not really a grinding noise, a loud audible groan.

I am guessing the pad is worn, it just seems strange that this noise only happens when I turn right and brake.

Any ideas ?

 

I would check your wheel bearings. If you drive in a straight line and swing the bar from left to the right repeately. If you hear the groaning noise then its your wheel bearings. If your rotors are full of rust, the brakes will make all sorts of noises. Brakes usually make squealing noise.