Thank you very much for the info. I'll keep it in mind for future reference, and it would be the least expensive way to go.
But, I'm going to return the observation car for a couple of reasons.
One, it's just not right that I should buy a brand new item and have to go to the trouble of repairing it because of a manufacturing error on Lionel's part.
Two, I limit myself to a pretty small train budget, so for me, the purchase of 7 Baby Madison cars (a 3 pack and 2 2 packs) is an extravagant purchase that I had saved up the funds for a while. I know it isn't much money compared to what folks are paying for scale cars or Legacy locomotives, but I've wanted to get this set of cars for a few years and it's disappointing to finally get it and there to be a problem with one of the cars. The observation car is my favorite heavyweight car because of the platform on the end, so to get an observation car without the platform is particularly disappointing.
Third, I haven't been able to find much in the way of photos of the newer Lionel Baby Madison cars. All the dealers show the Lionel catalog picture, which doesn't show the platform end of the car. Looking at ebay, I see a dealer selling break ups of some of the cars from different railroads. Some of the observation cars for the Santa Fe and New York Central have non-illuminated drum heads on the end rail, while the Pullman does not have a drum head. I haven't seen any pictures, so I don't know if the Canadian Pacific observation car comes with a drum head or not. But, if I buy a generic observation gate and repair the car myself, I'll never know and it is going to bug me. As I said, this is an extravagant purchase for me, so if I do receive an observation car with a CP drum head, it makes the set just that much more special to me.