Just a little follow-up. I received an OEM 473313 bushing courtesy of HH56 and rigged up a primitive durometer using a scale on the arm of a drill press. The numbers represent pounds of force required to drive a blunt round pin of 0.20 inches diameter into the rubber for a distance of 0.250 inches. One variable than cannot be accounted for is whatever effect the age of the OEM bushings might have had. It would have been nice to have one of Kanter's bushings for comparison.

OEM bushing: 5.4 lbs.
Merritt new: 4.7 lbs.
Merritt old (with Steele logo): 3.5 lbs.

The repeatability of the measurement appears to be about +/- 2 or 3 tenths of a pound.

UPDATE:

Kanter bushing: 5.2 lbs.