Engine Oil Warning Light/faulty sensors??

Can you please help me I purchased new in March 2001 an S Class 320 CDI after approx 6000 miles I keep having the warning light show when the engine is warm, dipstick shows a level to the top of the stick or even just below, local dealer who I have spoken to many times says that the sensor is very sensitive and basicaly nothing can be done except daily check dip stick!!! why should this be on a car costing £50000. I now hve 10000 miles on the clock and the latest warning is red light warning buzzer and stop car now
but levels are OK. This is not good what can Mercedes do for me.