Oil pressure guage problem 1988 560sel

Need some advice here. Just took the baby out of winter storage and took it for a 30 miles drive - worked perfectly- the oil guage was pegged at 3 all the time except at idle when it dropped to about 1.5 at idle - all normal. Started the car to go home and noticed the oil guage was only at 2.5 not 3. As I drove the 30 miles home the pressure slowly kept falling to about 1.5 when I started to panic and tried coming to a stop to let the motor idle. The guage showed 0 but the engine sounded good so I revved it up and she when to 2. I continued driving at about 40 mph and by the time I got home the oil guage was only showing about 1.25 at 3000 rpm. I shut the engine off and started it again. The oil guage went to 2 at 2000 rpm. Shut it off and started it again - it went to 2.5. Shut it off and started it again - it went to almost 3 . Held the revs at 2000 rpm for about 3 minutes and it started to drop again. I sincerely hope it is a bad oil pressure sensor. Before I dash out to buy one - any one else have an idea? Sure is scarey when your oil pressure doesn't read right!