I do not know the VIN code stuff, but if you have a 3800 series ii engine (it will say on the plastic engine cover) Then this will apply to your car -
In front of the engine is where that sender is. There is this foil-like tube that serves as a heat shield. It is close to the thermostat housing, almost right under it.
Be careful when disconnecting the wire, it is a bit of a pain.
When you unscrew the this little sensor, you will lose some coolant, unless you have drained some of it beforehand.
I know this sensor sends to the gauge because I had a similar issue not long ago.
The repair is easier than changing the oil. Do make sure tho that there is no coolant still leaking out of the small orfice, try and dry the orfice best you can, and use a bit of sealer on the sensor.
1999 LeSabre, 3800 series II engine.