My understanding is that the oil warning system was introduced in response to the valve seal problems on the early inline 4 engines (early rabbits, etc.)  These seals could fail rapidly (sometimes after only 20k miles) and increase the oil consumpiton to the point where the engine could be destroyed due to low oil, even if you checked the oil at every fillup!  VW fixed the seals around 1980, settled a few lawsuits, and introduced the dual oil pressure system.  The new seals are ok, but seem to fail around 200k miles.

Bill

>I don't know what VW may have known about the 2.1 rods but from what
>I've seen they started putting the extra oil warning system in their
>cars starting about the 1982 model year. It is called the Dynamic Oil
>Pressure Warning System. They eventually phased it into the full product
>line AFAIK, reaching the Vanagon production during 1985 (model year
>1986). Waterboxers, inline 4 and 5, diesel and gas, turbo and
>non-turbos, all have it starting at some point.