I'm thinking we are all going on the theory that the brakes are not functioning properly now. I'm also assuming you have driven it and tested the system yourself. Letting us know what it is actually doing would be helpful.
Not to dis your co-workers, but I'm sure they have worked on very few, if any, hydraulic brake systems that use shoes. In other words, don't take someone else's word for what has been done and what is right or wrong with it. Go back over everything methodically and don't be ashamed to get out the books and follow them if you haven't worked on these before. Or even if you have and your memory is like mine. And remember that what is on there may not be correct since someone else has been into it. If the first guy did it wrong and everyone else has just put it back the way they found it, then that may be the story.
Like all trouble shooting problems I'd look at the simple stuff first. Brake adjustment, shoes on correctly (primary and secondary in the right place), glazed drums or shoes, brake bleeding, and vacuum to the booster all come to mind.
There is a filter in the vacuum line and the vacuum line probably runs to the pump as well, so I'd make sure the booster has vacuum before you remove it. The filter is located somewhere in the line, most often under or just behind the right front seat. The booster also has a vent that needs to be open. Mr. Mud Dauber may be in town, so you should check it. If the diaphragm is bad it will most likely blow blue smoke out the pipe from the brake fluid being pulled into the intake manifold.
My experience is they can be a bitch to bleed. They need to have the booster bled as well and I have found that doing that first works out best. I ended up using a pressure tank to force fluid through the system after trying conventional bleeding for the better part of an afternoon on mine.
I'm thinking the rear wheel cylinders are no longer available, especially if it is an E model. If so, I'd be pretty suspicious of the story that they have been replaced "multiple" times and if they have then they may be the wrong wheel cylinders. If it is an E model I have the PN if you need it. If it is an L model someone on here will have it.