My Park Ave was also giving me a high pressure reading 100psi and had a small leak as well.
Once I changed it, all is well with idle readings at 58 cold and 68 psi at 1800 rpm cold.
I would recommend using only the Delco replacement part for your 2000 LeSabre.

Ok I just chgd the oil,filter AND the sensor...great place to get to when its 11 degs out,,,,now it reads 65 psi and when I rev the engine it goes to 75....isnt that still too high ??

if you just changed the oil and its cold, your probably good

I have the DIC which displays Temp, Charging Voltage, Fuel stuff, Odo and Trip, and Oil Pressure - all in green LCD'*. My oil pressure has been reading 129-130 constantly since I got the car. The readout also says "Normal". I've been watching it like a hawk by checking the oil level before I drive anywhere. No problems there.

What I dug up on this (before I found this site) says this is a very common problem and is almost always the OP Sensor.. it could be bad, or just clogged with sludge or debris. Cleaning the openings (sensor and engine side) with a paper clip or wire may even resolve the problem but was highly recommended to replace the sensor anyway - still cleaning the openings.

When I took my car into the Buick dealer for it'* first LOF, I had them give me an estimate for replacing the Sensor - - $291.00 Parts and Labor ! ! I couldn't believe my eyes. They said that included diagnosis.. I know how that works

I'd replace it myself for almost nothing, but I have no way to elevate the car and get under it. It sits so low to the ground that even 9" ramps would not raise it enough for me to crawl under. My only other option would be to hit it from the side with the wheel and shield removed.