David -
I have noticed on several of my Kenmore machines that were out of service for a while that water level selections seem to now be lower than they should be, by one to two inches, most noticeable on the highest level. This I've noticed in two 1980 built machines, one a standard capacity and the other a large, as well as in a 1985 built machine with an infinite level switch.
With your machine being a 1977 model, the issue happening here may very well be the same. I am not really sure of the origin, but it would seem that the pressure switches are becoming less sensitive to the different settings, or they are not reacting to the changes in set position as much as they used to.
There is an adjustment screw on the switch itself, however I am not very keen on messing with them in these cases, not yet anyway. Should we adjust the screws then the switch itself regain it's original sensitivity later on, we'd have a possible overflow.
My thought for now is to check each switch and be sure that the adjustment shaft is properly lubricated, and that diaphram that relates to the adjustment is moving freely with changes in the setting. It is possible that a cleaning with WD-40 or similar and a re-lube with white lithium on the adjustment shaft would fix the switch's sensitivity. If not, then we can mess with the adjustment screws.
Are you able to look at the switch in your machine?
Gordon