Hey guys, I had the SAME exact flickering problem on my 2004 325ci. Problem, at least in my situation was NOT any sensors, o-rings, etc.
The problem is the weight of the oil being used. The light is telling you that the oil pressure is too low...
HOW TO SOLVE:
1 small bottle of STP oil additive. It has a very high viscosity and will thicken your oil. This immediately fixed the flickering light as the heavier oil raised the pressure sufficiently. Note, this is only a temporary fix. Consider it a band-aid until you change your oil.
Oil change with a heavier weighted oil. I was running Full Synthetic 5w-30 (which is what steven's creek BMW recommended), and that seemed to be too thin. I changed to Mobil1 0W-40 European formula full synthetic during my oil change and it fixed the problem! A year later and I have never come across the light again