This thread inspired me to take the plunge.
I took one of my drums apart and it's not super easy to get it back together, but doable. Refer to the manual's drum diagram for the part names I'm using.
http://www.pietta.us/pdf/MAN PPSPUMAweb.pdf My drums came soaked in oil as well and I found there is oil on the plastic rotor inside. I think it would be a good idea to get that off, not to mention when cleaning the drums after lots of firing I would like to be able to strip and assemble them.
So the main issue when reassembling the drum is that the rotor spring needs to have enough tension on it when you put it back together or you can hear the rotor rattle inside, the other drum I didn't take apart you can hear the spring but not the rotor. Another way to tell is by using the loading tool to depress the follower/dummy rounds, they should snap back up to the top if there is enough pressure. It's a little finicky getting those dummy rounds to sit right when reassembling the drum. It's best to spin the rotor until they rounds are sitting in the proper position before continuing. There is also another pin (not shown on the manual's diagram) which holds the inner part of the spring on the center pin, make sure that the end of the spring is in the slot in the center pin, put in the pin and make sure it is flush.
There is a tiny block pin that sets the tension when put in one of the four holes in the center pin. You basically need to spin the center pin around from the rear side using the magazine plug and hold it until you can put on the front cover which locks the block pin in place through a hole in the front cover. Then you put on the other magazine plug which secures the block pin in place from the other side. The front mag plug has a groove on the underside where that block pin fits into. The rear plug doesn't have this groove.
All I did was crank it around as much as I could, dropped the block pin in the corresponding hole in the center pin and then quickly put on the front drum cover and then the front plug. If one of the dealers can find out from Pietta the proper factory tension on the spring that would be nice (how many turns to set the tension). I imagine though as long as there is enough pressure from the spring to feed the rounds you should be okay.
Hopefully I can go test this puppy today and see how both drums function. I'll let you guys know.