Martinjmpr,
Chances are it's not your rear wheel cylinders. That's not a common issue on these vehicles, but leaking rear axle seals are VERY common. In either case, the leak would look very similar, but again, leaking wheel cylinders are far less common. Check out this thread... it's a write-up I put togther for the rear axle seals. It might help you diagnose the problem.
http://www.toyota-4runner.org/3rd-gen-t4rs/67299-rear-axle-seals-ultimate-information-replacement-thread-3rd-gen.html
I did my rear brakes when I replaced the axle seals and it wasn't bad at all. I had to buy a pair of brake spring pliers, which look like needle nose pliers but with hooks at the tips of the jaws. They allow you to get a firm hold on the springs that hold the shoes together so you can easily remove/install them. Also, there is a tool called a "Hold Down Spring Tool" that you can get at most auto parts stores for $5-10 that you'll need to remove the hold-down springs that secure the shoes to the backing plate. (You can see the hold down springs in the 3rd and 6th pictures)
This job is definitely more difficult than doing the front brakes, but just get yourself a haynes manual or you can access the Toyota Factory Service Manual (FSM) here>>>>
http://www.ncttora.com/fsm/1996/SIL/fsm/repair.html
>>> and it'll walk you right through it. Note that toyota will refer to the tools you need as SST's.
Also, I bought some rear brake shoes from Autozone, their Duralast brand. Well, long story short, these shoes SUCK! They don't fit very well. There is a pin that retains several of the drum brake parts to one of the shoes. Not only do you have to drive this pin into the pad yourself, the spine of the duralast pads was too thick and the pin didn't extend far enough through the spine to attach the C-clips that retain the other parts.
I ended up buying a rear brake shoe kit from Toyota. The pins were already pressed in, it came with all new hardware, an the shoes fit perfectly. I guess that's why the Toyota shoes cost $68 Vs. $14 for the Autozone shoes.
Here's a few close-up photos of the passenger side rear brake assembly (driver's is the same, but the shoe assemblies are on opposite sides), in case you decide to do the job, but forget to take pictures before you get it apart. I had both sides available for viewing when I did mine, so if I forgot where something went, I just went around and checked out the other side.
The pin I was talking about above is located near the top of the photo, just right of center.
