Engine oil warning light coming on

Just bought a car and the engine oil warning light is coming on.

Background:
- An oil leak was recently fixed (new cam and crank seals fitted)
- The dipstick indicates oil level is to the maximum.
- I had the oil pressure switch changed by a mechanic after the first time I saw the warning light come on. As soon as I told him the issue, he checked the oil which was full and made an assumption the pressure switch was faulty but I don't think he did any other checks. He said that should fix the problem.
- The warning light comes on intermittently. It came on the third day I drove the car, and again today (only had the car 2 weeks).
- Reading the service history, the oil pressure switch was already changed 9 months ago (maybe the seller was aware of the issue?)

Anyone know what the problem could be?
It's a Daewoo kalos car (i know they are terrible cars! :frown:)

Have a shop install an accurate manual oil pressure guage in place of the sender to check the engines actual oil pressure against manufacturers specs. Could be oil pump, pick up screen,bearings.