Here is a starter for you for Takumar in general.
Favorite Classics / Pentax Super Takumar f/3.5 135mm
Main difference is that the 200 splits at the join in the middle of the lens which will give you front access to the blades.
Here is another Takumar lens by way of comparison:
http://homepages.ihug.co.nz/~Srawhiti/pentax50mmf1.4.html
This aperture switch fixing site is in Chinese but will give you some pointers. The issue here (apparently) was more one of lack of tention in the sprongs in the mechanism and as that requires a new part it was an unsuccessful attempt. - Google translate does an interesting job - not standard English however.
Pentax M42 135mm f2.5 Ãè*ײz
Good luck
Last edited by Arjay Bee; 07-05-2010 at 05:49 PM.
Reason: clarification