Low Oil pressure Warning

Got out after winter storage and found that a couple of minutes after starting the oil pressure warning appears and the buzzer sounds. Dropped sump checked sump/sump filter were clear,Changed oil and oil filter but to no avail.
Tried to read through topics - are there two pressure sensors on the 1.8 non injection? GSF list three 931VG0030, 931VG0050 and 931VG0050 (White) I am planning to change the pump and sensor(s) anything else it could be and which/what sensor should I buy.

I would add I have recently changed to oil filler cap for a replacement from GSF this would not have any effect would it?

Thanks

For a start, don't bother buying one from GSF or Euro car parts, they are tosh.
Order a low pressure sensor from VW main dealer, to confirm it is this that is shafted, disconnect the wire from the sensor located by the oil filter, and connect it to the little spare spade connector on the side of your distributor housing, basically earth it out.
If it still carries on squealing, its you clocks that are shafted not your sensor.