Can you please give some more details so I can tell you if it is worth doing or not.
The older Crown Edition(approximately late 1980's to mid 1990's) passenger cars with fixed couplers need total truck assembly replacement if they go bad.
If it says Williams Reproduction you have a better chance of needing only the roller assembly and not the whole truck.
Williams by Bachmann can use most of the same parts as Williams, the only exception is early Williams before the DC can motors.
There is a person in the state of Maryland who has parts for Williams Trains. I don't have his info but somebody on here does.
Lee Fritz