jlehmus
I don't think the camera is defective.

Minute variations in the camera's part's specifications will account for this. And it's not only in FED-2 or -3 that this happens. I've seen this happen in almost all of my III-series Leicas, some of my FED-1 and Zorki-1, and even with my Praktica SLRs as well. I don't find them offensive at all- in fact, I often like the effect, the sort of "charming characteristic" you mentioned in your blogsite.
There are tricks and remedies available to relieve this slight frame to gate misalignment. But most of these involve clumsy modifications like using spirals under the cassette and takeup to push these up.
And with transparencies/slides, I must say that I've never had a problem with them too. Most of the slide frames have really smaller windows compared to the actual frame size on the film. The slight misalignment is often hidden under the frame.
JJ