Thank you for the detailed answer. I looked up some basic folder designs on the Internet and was able to restore my 533/16 BX. I unscrewed the back lens element with my hands (didn't have a lens spanner wrench), opened the shutter and cleaned all elements thoroughly using distilled water with a drop of dishwashing soap and a lot of Q-tips. Then I removed the focusing ring and unscrewed the front element and cleaned those surfaces as well. There was no need to remove the second element, as I could get at it from both sides. I loaded some wax paper on 120 rolls and used this as a ground glass to recalibrate the focus at infinity (courtesy of David Richert). Now all I have to do is put a tiny bit of lubricant onto the gears and helicoid (it's not as smooth as I'd like it to be), repeat the calibration and shoot a test roll. I'll also give the leatherette a nice rub and shine up the metal parts.
As you can see on this test shot (before), the focus (infinity at 5-8m) was off by a large margin and the grime inside the lens had a very visible impact.
I will post some test shots when my work on this camera is complete. I don't want to stop here though. I'll get the suggested readings mentioned in this thread and turn myself into a semi-qualified repairman.