In looking more closely at the controller board, I found that the 2 humidity
sensor leads are tied directly to the 87C809 uC pins 6 and 7.
Between the #6 and 7 pins there is a 1M ohm resistor (meas 994k) and pin 6
has a small smt cap to the circuit ground (-) of supply.

There is no reason to expect that the dehumidifier will last for several
years, even if the sensor is replaced, which may only mean that the sensor
may need replacing again next year.
There were numerous reported failures of these models after one year, so a
repair that returns the unit to a "good as new" level, only means that it's
likely to fail again next year.

The sensor manufacturer's specs show a voltage rating of 1V, and I've seen
4V AC present at the sensor (the sensor resistance decreases as humidity
increases).
I don't know, but I suspect that this may have caused a change/drift in the
sensor's characteristics.

This exercise in frustration is another example of the present level of
quality of consumer goods.
The race to the bottom has led us to the point of new levels of
consumerism.. where it's unreasonable to have any expectations of quality,
and the stores are always full of new crap to replace the old crap.
Shopping for new crap has become a form of recreation, at least here in the
US.. they can't build malls fast enough to satisfy the cravings.

This dehumidifier was essentially produced with the lowest cost parts
available (the electrolytics are 85C rated in an appliance that will
generate a lot of heat) which are then assembled with lead-free solder, and
rushed to a store near you.

This is the primary reason why I quit repairing stuff, even for friends.

--
Cheers,
WB
..............