I'm working on a Rixe folding bike. The Sachs Torpedo Duomatic hub is a '69 model, and I presume it's original to the bike. It has a new-on-me crank -- this crankset has a cotter on the NDS and...nothing on the DS. The DS arm and ring seem to be swaged together and I can see what I presume is the end of the spindle protruding through, and ending flush with, the crank arm. There is nothing obvious that fastens the crank arm to the spindle. The NDS arm has a conventional cotter. But the end of the spindle has a strange triangular "hole" in the end. There's a large hex nut just inboard of the NDS crank arm.

I'm guessing that the NDS arm is fastened to the spindle with a conventional cotter. Once the NDS arm is removed, I'm guessing this nut is removed, and the DS arm and spindle assembly slide out from the DS? Sort of like a strange combination of an Ashtabula crank and a 3-piece crank?

I like to get the cranks off this bike frame, as I'd like to give it a deep clean and fresh paint. But I also don't want to fix something that's not broken, and I'm wondering If I shouldn't just leave this whole contraption in place. The bearings sound dry, but they're also smooth and seem to be adjusted well.

Thoughts? Ideas? Dark tales portending very bad things if I try to remove this crank?