Can sympathise with your buzzer probs as we had similar. We've also got a 1.9 diesel 1Y fitted (came from 98 Seat Toledo) that was put in our van a couple of years ago - well pleased with the conversion though, when it is working properly!
Basically fitted a VDO 0-5bar oil pressure gauge and 2nd hand sender from a vw coupe (95 I think it was?
). Took out the orig sender that sits on top of the oil filter, screwed in the 'coupe' one in place of. Then ran a wire from the new sender to the dash board, where mounted the vdo guage. Got volts to it and then presto! ? You can now watch what's going on engine oil pressure wise and not be worried by any false alarms.
All best with it though!
Cheers.