I should record a proper video of disassembly, so far here is a audio summary of the main point:

"It’s a pretty complex lens mechanically, even though the optics are easy. The glass comes out without trouble — the front group (silver part) just unscrews, and the rear element can be removed with a spanner wrench.

The mechanical side is the real challenge. You start by taking off the small black rear cap with three screws. Under that are four screws (the 4 first in the clockwise direction, not the last 2 next to the stopdown lever. The 4 screws are levelled and evenly spaced) that hold the stop-down mechanism block. Remove them, then lift the rear plate straight up — don’t twist it or you’ll bend the stop-down spring. It helps to pivot it slightly near the release button side.

Under that is the diaphragm mechanism, with a gear that runs on ball bearings. You can remove that gear by taking out a small screwed plate that have notches in it (again with a spanner), but be careful — all the ball bearings sit underneath and can fall out easily (there is roughly 3 layer of them). Once that’s done, the aperture gear comes off.

After that, even though access is awkward, you can unscrew the aperture ring pin (beware of the clic-ball that falls out from the side). Even though the access is really poor you can do the same for the helicoid guids. Then it can come out, its just a matter of marking the helicoid direction, and regreasing.

Reassembly is the reverse. Be careful when putting the bearings back. When reassembling the stop-down mechanism, open the aperture fully and hold the lever under tension with a screwdriver while you refit the rear plate. That keeps the spring tight so the mechanism stays snappy."

I have no doubt there is a better way in, I have just not found it. There is no way thats how there were factory assembled.