> even with that small amount of current, Joe?

The internal diodes vs external Schottkys has been discussed in
depth before but I honestly can't remember the figures. Personally
I just don't like the risk. Another problem I've encountered once
was noise caused by machinery that got through to Vss. I didn't
investigate but perhaps Vss rose relative to the inputs. Schottkys
did prevent any more PICs burning out

> Been using dimmers with a 1Mohm straight to a 16F pin for zero-
> crossing - nothing else. makes some 400uA... working for years

The waveform is centred about Vss ? The internal pull-ups have
around 400uA pulling power, maybe yours is a safe current like
that
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