Hi,
Just a quick note for the record on a problem I recently had with a 1.4 Diesel 106. For (too long) now the oil light has taken ages to go off on a cold start, and occasionally (maybe once or twice in a month) flicked on for a second whilst running. Everyone (including professional mechanics) had said to me "Must be electrical, oil lights tend to come on when the engine is hot if there is a problem". Replaced the pressure sender, still the problem was there. Flushed the oil system, replaced the filter etc etc. In the end took the sump off and the pick-up strainer was almost completely clogged with excess instant gasket which a previous mechanic had used to over-enthusiastically seal the sump. Problem solved.
Hope this helps somebody else,
Jon