Busch Pressman - how to lube rotating back?

I picked up a pretty nice Pressman D for small money a while
ago. The back rotates but is very, very stiff. I don't think
this is normal as one shouldn't need three hands to turn it;
in its present state the rotating back feature is not terribly
useful.

It would seem some lubrication is in order, but here's my
problem. It's totally unobvious how the mechanism actually
works since all the surfaces I can see during rotation are
basically flat. I tried a very light film of moly grease which
didn't seem to help. I assume there's something inside that
really does the work, and is where the lube should go.

If I rotate the back to 45 degrees I gain access to four
screws in the corners, which I guess hold things together,
but I'm nervous about disassembling it in case it's massively
spring-loaded - the last thing I want/need is bits and pieces
flying all over.

So far I haven't found any disassembly pictures or info on
the web. Has anyone ever operated on one of these and
documented the process? Better yet, does someone have
access to a factory assembly or service manual?

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