I made a guy pull a 904 and bring it to me once. He had broken a rear, fixed it, and was driving the car around on the street. Everything seemed okay and it was going to the track. I insisted he pull it.

Half of the springs were mashed flat by the rollers when the rear broke. The rollers were loose in the assembly. The other half were still functioning enough to drive the car around. It would not have survived the first hit.