I do not have a picture, but it is attached to the lower front of the block, directly beneath the waterpump port where it goes into the engine. (Directly to the right of the dipstick mounting bolt. My engine is greasy as hell around there, and while I have the engine exposed I would like to replace the seal if I need to.
I am replacing the water pump right now, and I noticed a little leak around the seal where the pump goes into the block and found the O-ring inside the facing was all cracked up.

 

Photo shows 1 of the 2 water pump/block flange o-rings. If the new pump didn't come with a new o-ring get another and replace both. The sensor you are asking about is the crank position sensor. There is an o-ring there and another on dipstick tube.

Inspect your thermostat housing for weeping/leaks while you are doing this job too.

Jeremy