Dragging left rear disc brakes

Yes you are on the right track. Flush ALL the fluid. Will take a few quarts. Pressure bleeder is preferred. Closely inspect the rubber hoses or replace.

John Deere would be no help. They sold that part of business to Oshkosh which was bought by Freightliner. Another poster gave me all the part numbers on an older post I made. The brakes front and rear are Meritor.

Thanks to all for the information. Total brake overhaul including hoses would probably be safest bet. All were getting a little warm but only left rear got smoking hot, literally.

Also, the Master Cylinder has "bleed" ports in it. When you release the pedal, fluid returns to the reservoir, through two fairly large holes, one for the front brakes and one for the rear. Those holes approach 1/8" in diameter. BUT there are also smaller holes, straight pin size, forward of those. They make sure all pressure returning from the calipers is bled off once you've let the pedal up. I've seen those rust shut and when that happens the brake stays partially applied.
But, typically, that will affect both brakes on that end. Both fronts and/or both rears.
So, how's the opposite rear brake acting? Getting overheated too?
Hoses are an often-overlooked suspect. Gotta say, I haven't seen a REAR hose actually block up like front hoses do, but I still replace the rear hose on a vehicle that leads me to think it's time for the front ones.
We had a school bus on Ford chassis with a dual braking system. Two hoses to each wheel, each pushing its own wheel cylinder on drum brakes. A steel bracket held the two hoses away from damage by the wheel. The steel rusted, and the swelling rust crushed the hoses shut from the outside.
Sounds to me like you'll probably end up working on the calipers. When I read John Deere RV chassis, I usually go look at a different thread, but I just finished working the "Kodiak" brand disc brakes on a boat trailer. The Caliper Casting might have been uniquely Kodiak, but the brake PADS were Buick, and the Caliper Piston no doubt was a common diameter. Likewise the slide pins and bushings probably fit something else. You might try an established NAPA store, where the staff has some parts experience. NAPA often has more catalogs they can look into, not just the computer terminal at the counter. I"m thinking you can get Hoses, Caliper Piston Kits, and Pads without calling them John Deere.

It does sound like the brake hoses, I've had this problem more than once.
The hose is a double wall design, quite often the inner seperates from the outer. The inner hose collapse's and is pushed open by the forcing of fluid through it when the brakes are applied. Then when the brakes are released and there's an absents of pressure(fluid) the inner hose collapse's trapping some of the fluid on brake pad/ shoe side; making the brake stay engaged with the drum/ rotor.
You can confirm this by seeing if there's fluids under pressure at the bleeded valve. Just to remember, that this can last a couple of seconds to a couple of minutes, or longer.

The caliper pistons or the slide pins could be sticking.
There could also be an issue with the rubber brake hoses delaminating internally.That would cause the brake fluid to flow one way and keep the brakes applied.

On a vehicle that old, I would do all four calipers and the connecting brake lines.

I just did my rv's brakes after fighting the same issues on three different calipers.

It could be the rubber hose too. I have seen them swell to the point where you can step on the brake and because of the swell inside the hose the pressure doesn't release as it should.