Oil Pressure reading ZERO

[mroliveira]

Hi All,
I have a 1993 300SL with only 94000 miles. When I start the car, all the lights in the dash light up, including the low oil pressure light (this is normal).

After a second or two, the oil pressure goes to 3 (again normal).

The problem is, after about 15 minutes of driving, when I come to a STOP with it still in DRIVE, the gauge reads between 0-1.
I've checked the oil level, and even had the oil changed, but it's still the same. When I gas it up, the pressure goes back to 3.

My assumplion is any reading of ZERO can't be good.

Where do I go from here????
Thanks for the input.