The yellow oil light comes on occasionally (maybe once a week) for a few minutes in my 88 300E. I checked the oil level in the dipstick and it is full. The oil pressure is always fine. Is this common among these engines, or is there something going on? Thanks for any replies.

Try removing the connector and cleaning it a bit. If that doesn't help, then you may need a new sensor. Buy it here for about $35.00

Before you go buying a sensor be sure you don't have a dash problem. Because oil levels change relatively slow they built a delay into the warning. This prevents the light from coming on during hard cornering and braking. The light only comes on after the signal has been there continuously for some time. I don't remember the interval, its probably less than a minute.