So I've been using those 1 gallon pickling jars for STB extractions and was wondering how many times one can reuse these jars, I have carried out 2 or 3 with this jar and think it would just be safe to go buy a new one. Am I just being paranoid?

Not paranoid, just carefull

Over time you will find that the lye could make the glass jar a little weak. If you are in doubt about the strength of the jars, get new ones and stear clear of any unwanted spillage/accident.

Yeah I think I'll just buy new ones and be on the safe side, I can see what appears to be very tiny cracks or cuts inside the glass.

Ye man, sounds like time to bin those jars and get new ones.