I got this together with my new LOMO R15 (ЛОМО Р15), the iris diaphragm inside was broken, so here a quick note on how I repaired it.
I started with dissembling everything, in order to get the diaphragm out the two levers need to be unscrewed as well as a small set screw on the bottom needs to be removed. I also disassembled the mirror part for cleaning.
The diaphragm was completely sticky due to dried up grease, so I carefully disassembled it and removed all grease remains using WD-40. I then carefully reassembled it.
I then applied some oil to it for lubrication (I rather have oil out than dried up grease stuck on a diaphragm) and reassembled the whole thing.