Two things- no need to open up the aperture section. Really, just don't. Life is short, don't do that to yourself.
Second, find a nickel. And a dime. I think a 120 spool will fit into the lens tube from the front. Then put a nickel in the blade opening (or maybe it's a dime, I forget) to fill the little space. this keeps the blades from tilting down into the opening and coming off the pins.
And no matter how bad it gets, it can be done. Slow, patience, and just accept that it will blow up a few times. Be sure to remove the ring that moves the blades and give it and its groove a good cleaning. THAT is the source of most problems. Make certain when you reinstall it to engage a spring or two properly in the front.
(check the X/M sync switch lever for that washer and spring that showed up. I'm not certain, but worth a look.)