Final update on the oil sensor:
I removed the old sensor and made an attempt at bending the tabs over and opening it up to get to the inner ORing.
I tried grinding those 6 tabs, and it was such a royal pain that I finally gave up and ordered a new sensor:
Here is the new yellow one compared to the old metal one (which may have been for another Buick model):
The new yellow one has a rigid shaft, wheras the old one had a flexible one:
Got it installed, and it does not leak, and appears to work:
Now, on to other repairs.