Okay, now did you ever replace the front pads? You should wear out front pads MUCH quicker than you wear out the rear pads... if you're front pads are find and you're still wearing out rear pads, you've got a problem in you're master cylinder, it's putting more pressure on the rear brakes rather than the front when it should be vice versa. I do'nt know much about the e-brake systme though, sorry.

 

Yes there should be a return spring on both rear calipers, check to make sure the e brake cable isn't binding, they tend to rust inside the casing and
will hang up a little, eventually completely seizing, keeping the brake applied, this is common on cars where the e brake isn't used all the time

 

Your car will have a Proportioning Valve on it someplace. Depending on the set-up and if you have ABS or not ... there will be a "Proportioning Valve" ... which keeps most of the Brake Pressure from the Master Cylinder going to the front Brakes ... or, a "Combination Valve" ... same story including the connection for the System Light.

If the Proportioning Valves went bad you have had the rear Wheels lock-up on you at some time or another. With most of the Braking forces needed forward on the car ... the proportioning valve does the work of keeping the hydraulic pressure more to the from and less to the rear. If is sticks or fails ... the pressure isnt regulated and the rear wheels will lock-up on you.