[Shotimes] ECT Sensor questions!

[Steve Tatro]

I decided to replace my ECT over the weekend.  I'm not sure mine was
bad, but it's original (167k miles), my fuel mileage is nothing
spectacular (19mpg combined with a heavy foot) and the SHO just "seems"
to run rich (I have no data or reason, just a gut feeling).
 
Anyway, I bought the NAPA part.  It appears to be all plastic, where the
original Ford part was metal.  Should this concern me?
 
Also, I noticed something on the metal threads of the original part.  Is
this some sort of thread sealant?  Should I have applied something to
the threads of the new sensor?  I didn't, and there aren't yet any
leaks, so maybe all's well that ends well?
 
Thanks,
 
Steve Tatro 
Red/Black '93 with 167k miles 
Cincinnati, Ohio