Terribly uneven pad wear

Gday,
 
I drive a 97 Bathurst and the rear pads are wearing horribly. Specifically, the inside pads have worn much faster and also at an angle. On the passenger side, the lower edge of the pad (edge closest to the centre of the rotor) is worn down to metal while the top (at the circumference of the rotor) still has material left. On the driver side, the leading edge of the pad is worn to metal while the trailing edge is still pretty much new.  The outer pads on both sides still have well over 50% left.
 
I'm waiting for new pads/rotors to arrive so I'll check the calipers out then. In the mean time, should I suspect seized slider pins? Or does it sounds like the calipers are stuffed and need to be rebuilt or thrown in the bin?
 
Also, I used high temp wheel bearing grease on the pins when I did the pads last time. Couldn't find any grease specifically for calipers. Maybe that's the problem?
 
Cheers,
Adrian

Possibly a seized piston or even perhaps something hand brake related (i.e. your hand brake not fully disengaging)
 
Rebuilding capliers is pretty cheap, or if they're genuinely rooted, get another set if required.

As others have mentioned it is rebuild time for your calipers. They will have gunk in and around the piston for sure anyway. At the same time they should check the sliding pins for you anyway.

Caliper reco is not too hard to do if the pistons and bores are OK (I cleaned and polished mine), but you may need the right tool to rotate the pistons.
 
I got caliper kits with all seals, rubbers etc from Lithia Toyota.
I did both fronts and rears while I was at it, but you can get a kit for the rears separately.

From what you described, I would also check that the mounting brackets/sliders are not distorted and line up OK when you re-fit  the pads.