Remove the rear tires and check calipers for leaks. If there is a hint of a brake fluid leaking, the calipers are bad.
They are not too hard to rebuild yourself (I did mine). If you are not comfortable with rebuilding them yourself, replacement with new calipers is a simple do it yourself job. Of course you have to bleed the rebuilt or new calipers. Some will bleed by gravity and others need the brake pedal depressed. This takes a second person.
If the brake pads are more than 1/2 worn out, you might as well replace them. Also check the hoses for leaks and replace them if any leaks are present.
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