I had the " O " ring , blow out of the 45 degree elbow , at the back of the HEUI pump ( 3 times in two years ) that fitting and O ring are under the same pressure as the sensor .
I was using generic high pressure/temp " O " rings , the cure was to purchase the O ring and a new fitting from Cat , O ring cost 5X as much , but 4 years later no leaks.
If you've been using Cat O rings as the replacement , I'd say maybe time for the sensor to be replaced.
I have a LARGE pdf on the 3126E , I'll flip through looking for a torque spec.
EDIT: Found the spec in time to add it here .
10 +- 2 nm. / 90 +- 18 inch lbs.