With the viewfinder and lens capped, try leaving both cameras in a sunny window, without UV filtering, for a week or so, and then retest for improved readings.
Sometimes these old cells benefit from such exposure and I routinely give my Weston Master V meters this treatment, along with a few others, though these are in good shape and I've never seen a difference in my kit.
Two Master V meters had 'new' cells installed by Quality Metric's, George, in '06 and I hope never to be without them again.