Basic tear down video so you know what your looking at. Given its old it probably wont come apart that easy.
Take off the top piece. Take out the adjustment set screw (on the side not the bottom, but if the bottom comes out try). try to get the pistons to fall out (try to remove like ketchup bottle). Don't force anything as there is an easy way to get stuck ones loose, its usually the little one that is stuck. start to screw your tank in and stop, then find a rag or blanket, screw the tank it enough air pressure leaks out (this is mildly dangerous don't cover the opening with your hand. Now you direct the open end into the blanket and it will shoot the little piston out. Unscrew the tank and collect your prize. If you use CO2 make it quick and use gloves or hold on with rags, CO2 will freeze things up.
Now look at your o-rings there are 2 on each piston, if they are undamaged use some kind of paintball grease like you would every other regulator. IF they are broken go to the hardware store and find some orings that work or try to look for a kit (which If I knew the sizes off hand you could just order those).
Last the washers are called a spring stack. Put them back on like the, )()()( , They are bent with a curve to act like springs when assemble correctly. It doesn't matter how many there are as they always begin and end the same.
Also if that is all too difficult you can get them "new" which is is remaining stock I assume for $25 or less.