Unscrew the petcock and put a drill bit in a tap holder and start twisting….you’ve got a buildup back there. Not uncommon at all- even after having your block “professionally” cleaned.

Question- were you ever able to get water out of the peacock? Might be old scale buildup, and not Bar’s.

I used Bars once in my life- it glued the heater valve shut in my car. After that, I never used it again.

~ Dave
1950 Chevrolet 3600 3/4-ton with 261 engine & T5 Transmission