Bill T,
Nice fix, however I took the tank Flat Car and replaced the trucks and couplers with the MTH Premier truck sets, it adds the weight needed and the quality trucks make the tank flat car run perfectly, and the couplers operate correctly. If I purchase any more of these flat cars I intend on doing the same thing, ends up costing about $22.00 for a decent flat car with load.
PCRR/Dave