Resurrecting this older thread:
I just spent a surprisingly easy half hour or so fixing the double exposure prevention mechanism on my Perkeo I, thanks to Hans's Flickr set in post #19 above. I wanted to give credit where credit is due. Upon removing the top, I found that one of the springs controlling the mechanism, the one indicated by the green arrow in slide 15 of the Flickr set, had become unhooked. Small wonder that the mechanism would fail to disengage at random times, essentially making the camera unreliable and thus unusable. (I also found the clear covering for the "arrow" window (see post #15) under the top deck; that might have caused some jamming too.)
I found that the focus was off significantly at the film plane. This was an easy fix -- a matter of finding the correct infinity focus with a groundglass (matte finish Scotch tape, actually), loosening the three grub screws on the focusing ring, turning the focusing ring to infinity (while taking care to not turn the front element), and retightening the screws.
So because of the unreliability of the double exposure prevention mechanism and the bad focusing, I had basically shoved this camera into a box a few years ago. Now I plan to give it the fair chance it deserves!