Did you try cocking the shutter first, then adjusting the aperture? One of my Canonets exhibits this very behavior when the shutter isn't cocked, but the effect is nearly negligible when it's ready to roll. While I'm sure it's due to a bit of gunk somewhere, it wasnt enough in and of itself to be a "send away for repair"-worthy issue.

Since then, events unrelated to the aperture blades have me considering sending it out for a full CLA, but if that were still the only factor, I wouldn't be sending it out.