I'm well over due for a tune up and possibly i also have a bad o2 sensor wanted to know if the bosch sensor when be a good replacement. Second I pulled off my distributor cap and found that the inside was completely covered wit white chaulk, can any body tell me how's that possible. Thanx

 

I personally have found the Bosch O2 sensors inferior to the AC Delco or Delphi brands & I believe others here have had problems with Bosch.

The white stuff in the cap is the oxidation / corrosion of the aluminum contacts. Get a cap with brass contacts when you replace it.