HELP, OIL LEVEL INDICATOR FLASHING with NO REASON

[ALEX 500SE]

HEEEEELP!!!!
When i start the engine, everything seems fine, but when i start driving and doing over 30-40MPH with constant speed, the oil indicator starts flashing like oil level drops. I checked oil level seems fine, just over middle,- between two markings. I bought my Merc 3 months ago and first time i noticed this when i was doing 70MPH,so i toped-up oil level to required level thinking that was a problem. The previous owner told me to use Castrol 15W-40 (when i asked him about it he tryed to remember it, what makes me thinking he dont remember exactly which viscosity he putted in). Now i dont have to reach even 70MPH, before oil level starts flashing. Engine works nice and smooth, oil pressure on 3 bar at most of the time (briefly rises pressure on acceleration-cant be oil pump) Wanna try to change oil filter and oil, but dont know, should i use same 15W-40 or something different, or maybe my toy slowly dieing[V]

[guydewdney]

is it just teh indicator flashing - or does the pressure drop as well?

if just the indicator - i wonder if it is the sensor? there might be two - one for the guage, one for the light?

if reading low oil pressure, then it might be the pump is dying. also the cam spray rails have nbeen known to fail - causing low oil pressure.

first off - new oil and filter if i were you.

like NOW....

[ALEX 500SE]

Thanks for reply.
The oil pressure is all right, most of the time on max 3 bar. Only drops a bit down to 2bar when you switch into "D" drive, but when you accelerate it quickly goes up to max, looks like its not oil pump.
Spoke to Mercedes dealers, they say maybe its sensor which is playing up, but it's cost £32, i dont realy fancy to buy it and then keep it in a box if its not the problem.