How do you tell the difference between a plain 1991 Oldsmobile Quad442 and a W40 or W41 Quad442?

To begin, there is no "plain 1991 Oldsmobile Quad442." There are only "W40" and "W41" cars.

The W40 cars include the following:

1. On the doors, and running to the back of the car, are gold-striped decals. The doors also say "QUAD442."
2. On the radiator support, there is a W40 tag that is riveted into place.
3. On the spare-tire cover, there is a Service-Parts Identification tag, which will have all three of the digit RPO codes that were used to produce your car. This tag also the VIN and "W40."

The W41 cars are very similar but include some important differences:

1. On the doors, running to the back of the car, there are silver-striped, rather than gold-striped, decals. The doors also say QUAD442.
2. On the front fenders, there are W42 decals.
3. On the radiator support, there is a W41 tag riveted into place.
4. On the spare-tire cover, the Service-Parts Identification tag will say W41 rather than W40.
5. On the engine, the IDI cover will be painted red and will have W41 in the center. One edge of the cover will read "Exclusively for Oldsmobile."