How to tell a real Lionel 6520 w/ green generator from a repro?

I’m servicing a lionel 6520 searchlight car, and while looking around for a replacement searchlight housing I discover two things:

  1. This car has the rare green simulated generator (cool!)

  2. You can buy a green generator from parts suppliers.

Hence my question: How the heck do you tell if a car has an original green generator? THIS one I know to be original, but what if you were trying to buy one at a show, or from an auction house, or (gasp) ebay?

Good one, For me it would be hard to say, The only thing may be the color of the green if you know you have a real one

http://www.tandem-associates.com/lionel/lionel_trains_6520_operating_car.htm

http://www.postwarlionel.com/cgi-bin/postwar?ITEM=6520

If it has a green generator, the odds are that it is a reproduction.
I suggest comparing the green generator to one that is known to be either an original or a reproduction.
Look for a flaw in the radiator mesh.
Some reproduction generators have this flaw.

When the reproduction generators hit the market, the vendor was selling them as sets of three, one orange, one maroon, and one green.