An update on the A3. After installing the replacement oil pump the remaining job was to have the oil pressure tested using a gauge by my local Mitsubishi service agent. At the same time, I purchased a new OE Oil Pressure Sender and had them fit that too as they had to remove the old one to fit the oil pressure meter. The pressure test confirmed that oil pressure was within the correct operating parameters, and pointed to the sender unit being the cause of the Low Oil Pressure warning. The new OE sender was installed, and surprise, surprise, the LOP warning light was gone.
So, a few dollars spent for peace of mind. I have a suspicion that the cause of the low pressure warning was probably a broken earth wire on the original Oil Pressure Sender, which was then replaced by an aftermarket sender that did not not include an earth wire, so unsurprisingly, the previous owner continued to have the LOP warning. The replacement VAG OE Sender Unit I purchased (NZ$76) included a new earth wire and my workshop duly earthed that to the engine via one of the Oil Filter housing mounting bolts. Problem solved.
Buying the A3 with LOP warning was a risk, but the engine always sounded smooth and quiet, so a risk worth taking. The car has now doubled in value, but I think I'll hang on to it for a while as it has only done 117,000km and is in unmarked, original condition.
Yeeha.... 🙂