Solution to my focus problem:

Thanks to all for input. Here's solution told me by my tech.:

The adjustment he was referring to is the cutoff. I have already done that - turned the cutoff down and turned the brightness up. I also cleaned both the focus and cutoff pots. It is a bit of a balancing act, but it has improved the focus about as good as will be possible; the focus adjustment is now quite apparent and there is even a tiny bit of headroom - there is a point in the adjustment where the clarity peaks, beyond which it again goes out of focus.