As an update on this...
I managed to open up the lens and have a look at the blades.
One of them was a little bent and I had to work on it to get it as straight as possible - I guess it got bent while was in use and it came off the grooves. I then manged to assemble the blades back in place and they worked... for a little while... and then they came apart again after using the lens for a couple of tests.
I honestly have no idea why...
What I have noticed... the "helicoid" is plastic... the two halfs that are guiding the aperture blades are plastic... and there is no trace of some sort of grease or oil to help with friction over time... not sure if that is normal or not, but it seems odd that there is nothing to help with minimizing the wear down. Plastic on plastic parts rubbing against each other.
My only guess is that the plastic that is used in the key areas has loosen up, or wear down a little bit, just enough to allow for the blades to jump off the groves. Or heat/cold have affected them and tolerances are bigger now. There seems to be a little bit of play, no matter how hard you try to tighten that front ring - obviously not going overboard and stripping the plastic threads.
If the front ring is not tight enough or comes loose over time (again, it screws into a plastic sleeve basically), the blades will come off the grooves for sure. That is what keeps the guides for the apprture blades in place, tight against each other!!!
So, when you work on these lens, pay attention when you remove that front ring.
Quite disappointed with the construction of these lens
.
Does anyone know if the inside of the limited lens are the same? Or they are actually using metal parts for the blade grooves and helicoid?
I have the entire green ring collection... worried eventually they will have the same fate
.