Initial thoughts are that it is just low on oil, but has enough to put the oil pressure light out, and throw it about in the crankcase when running.
Option 1. Top up the oil until it appears on the stick, at least to the minimum. Fine if the stick, and sump, are correct. Have the stick or sump been changed, ever?
Option 2. Drain the oil, and add the correct amount, as shown in the handbook. This would check the accuracy of the dipstick.
I don't know how many different sumps have been available for these engines, but if a deeper one has been fitted, the correct amount of oil may not be enough, as the oil pickup might not be low enough.
May need a bit more history.