Do NOT remove 3 focus scale calibration screws. I actually did that when attempting disassembly. And luckily, I also marked the original position before that.

I tried to remove the front element group first. But the thread is some how locked and impossible to turn using my current tooling. So I gave up, and most cleaning does not need to remove front group.

Remove focus ring rubber. Take your time, it's a huge piece and might be glued.