Could someone with experience please give me a ballpark figure for a series
resistor for using a watch crystal (32.768kHz) with a PIC?  I'm not sure how
much drive level these things can take but two of them have bit the dust
already so appearantly it isn't ok to use them without a series resistor.

If it makes any difference I am using them with the Timer1 oscillator on a
PIC16C73.

TIA,

Ken