The head on my 1989 cabriolet was replaced approx. one year ago. Recent increase in oil leaking around sensor threads on rear of engine block. I question thatthis (disruption of threads) was done at that time. Threads are stripped in block. Can I drill, tap, and use fix a thread or helicoil without disturbing engine oil or coolant flow, or worse yet, both? Also, what size would I drill and thread out to? Thanks for any help or advise that you could give me.