"What's so special about it is that it has this wonderful, untouched patina," Nye said. "Some people think it looks grotty - that's not the point - the really rare cars today are the unrestored ones.
"Every car that's restored has lost a part of its history because it's been obliterated by repainting or by rebuilding. Nothing's been obliterated on this, it's just a beautiful survivor."
He said he did not mind if the car was bought by an individual or an institution, but he hoped it would go to "an owner who really understands and an owner who really cares".
Bonhams chairman Robert Brooks said: "This is my fifth decade in the business and it was the most exciting discovery that I've made.
"We've had a couple of cars that have made over five million pounds and our thought is that this will exceed that."
Brooks would not comment on where the car was found, but said he hoped the highest bidder would take it back to Germany to enable it to be driven again.
The car will be sold by Bonhams at the Goodwood Festival of Speed in July.
-AAP