Ralph
How many miles on this car?
Are you the original owner?
Hello Ralph
The problem you are having with the oil pressure is nothing new to Volkswagen. It seems that they use a very sensitive oil-sending switch, the spring pressure is very sensitive and in time, it will make the light appear. I am concerned about the oil you are using. Most imports recommend 5W30 motor oil. I suggest you check with VW and find out what they recommend. You should not use heavier oil if it is not recommended. I really think you have done everything right so far to correct the problem. Volkswagen does have field representative that answer questions like yours. Perhaps you can call your local dealer and request a call from the field representative. I worked for VW years ago and they really stand by their product and offer good solid advice. Even though this vehicle was purchased from an auction, without repair history it's hard to tell if there was other problems which lead to this incident with the oil light.
Dan
PS - If it offers peace of mind, install a mechanical gauge.
What you need to do is install a mechanical gauge and take readings at both an idle and approx. 2000 RPM and compare those reading to the manufacturers specifications. You will then know for sure if this vehicle has the correct oil pressure.
Another Expert agreed with the information and advice I previously sent you. There is no other way to verify oil pressure other then installing a mechanical gauge.
Automotive Management
36 Plus Years of Direct Automotive Experience