OK, I see now that manual-aperture lenses do just fine in video mode on my K-7. I was careless enough to be in P mode before, hoping the camera could set the aperture with dials; it clearly stops down when the video is taking place, which allows for dialing down aperture settings on the lens as the video is in progress. Time to go cross out some notes on previous posts -- again.
So now I've done it: the Rikenon and Vivitar, both very good performers, were brought in for their push-pull smoothness as video lenses, so the V's A-setting is nice for stills but less relevant now. That'll teach me for thinking I'm done learning :^)