To begin, it looks like no parts are BROKEN on yours but like the shaft just came out/off/whatever you want to call it, right?
I have the same problem with the rear drive shaft on mine. I have not returned it, I simply fix it myself. However, if I fix it so it does not fall apart, I have to reassembly it with the shaft telescoped far enough inside that it binds on O-31 and even slightly on O-36 curves (it sort of varies speed and stutters just a bit). I could live without the O-31 but not the O-36 - I bought it just to run on 36. anyway, I can set it so it will not bind on O-36, but only by leaving the shaft barely inserted, and then, after a while, it comes loose.
Set far in (so tight it binds on O-36), it will run all day on my loop with O-54 without a hitch. The cruel irony is when I got it I actually spent a lot of time cutting down the top of the cab by 3/16 inch and repainting it, so it would go under a low, low overpass on my O-36 loop, only to then discover the binding. Now it can't run on that but runs only on my bigger diameter loops on which I will never run it much. Default shelf queen, it is.