Mine are the same as yours. I never noticed the difference until now. I wonder when they changed?I could be mistaken, but I seem to remember that Super Off-road came with two different types of steering wheels. One was a hard plastic and the other was a slightly softer rubber wheel. I guess they changed them during the production run. That may explain the two different kinds of caps you've found. My wheels are the rubber kind.
Maybe that steering wheel I bought for the encoder wheels was from a conversion kit? I have seen some two-player versions of Super Off-Road.

