Is that a true drum brake or a disc/drum combo? Mitsu uses a "disk on drum" for the rear for thier higher end models. They have rear calipers and a drum like housing in the rotor for the parking brake. On those there is a rubber cap that acesses the adjustment for the parking brake. You sometimes have to loosen the brake with a screwdriver (Turn down?) to get the rotor off.
If it is a true rear drum, any mechanic should know how to do this as they are standard American made brakes (Japs don't make drums).
As for the fluids, I change mine 1/yr or every brake job if I'm lazy. It's really pretty easy to do and extends the life of the master/slave cylinders. I do have speed bleeders in, so it's even easier for me.