Ok, I removed the air spring from my Vector and started looking closely with a magnifying glass and discovered the Firestone part number is stamped on the upper band that secures the rubber sleeve to the top cap. It reads:
Part number - WO2-358-7199
There are cap and piston numbers as well:
Cap number - NBD 10183
Piston number (lower black plastic part) - NBD 10238
According to the online Firestone PDF catalog, the 7199 air spring part number does not exist. The cap and piston numbers are good, but they're not shown as being used together in an assembly. That must mean they are custom and only produced for Fast; explaining why they're more than twice as expensive as a comparable spring online.
A Firestone WO2-358-7073 is almost identical to the custom 7199, but the lower piston is aluminum. I'm not sure if trying this spring is worth the risk for saving $60?
Also, I discovered the color of the Firestone logo represents the composition of the rubber sleeve. I'm going to assume the orange logo on the M20 spring would be a much more tough rubber than average to withstand the abuse.
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