The milk car needs a 5-rail (1019 or 6019, modern 12746) specialized 0-27 track section to operate. (For 0 gauge track, use a UCS or RCS, modern 65530)
Magnet-only 0-27 track sections 6009, 6029, 6149, 5149, or 65149 lack the control rails needed to contact the slide-shoes and are thus incompatible.
N.B. There is also an accompanying platform for the milk car, but it is not strictly required.