There's very little to go wrong inside them anyway, why not just strip and clean it out?
There's a tapered "plunger" that is pulled when you apply the brake. on these tapers there are 2 rollers that push out the pistons, that then push the shoes out.
I've had numerous ones in the past siezed up, the grease gets all covered in poo and brake dust, and eventually locks solid.
easy to get to:
chock the wheels, handbrake off,
remove the rear prop shaft (you only need to take off the handbrake end, but it may be easier to undo the diff end first then you can rotate and move "up" the shaft to get a socket in there... 9/16"s size)
undo the cross head screw
remove drum (you may need to slacken off the adjuster to get the drum off)
remove the shoes (peel apart and lift off of the lower expander and the top one.... or maybe left and right, depends on what type of brake you have)..make note of where the springs go!
undo the linkage to get the cable off of the expander, then there should be a spring-steel "staple" that just slides off of the back of the expander, it should then pull free.,
clean it up, degrease etc, re-assemble with a little bit of grease in there, re-assemble.