We (well Richard) suffers from this - will have to give some of these a go. Like you Ermintrude we reckon it's the rubber actually coming off the wheel...
Sounds like the surface has worn away. The stuff inside / under the protective surface is not suitable and will continue to give you this problem because it is soft. The original surface can be worn away by abrasion and rings over time but certain cleaners and solvents can speed this process. In theory it might be possible to use some sort of paint but I havnt found one yet that works long term. Once its gone the only answer is a wheel cover or a replacement wheel.
Sounds like the top coating has worn away. It's not dirt, gave mine a good clean and LIGHT sand with wire wool, made sure it was completely dry then painted in black hammerite, did that 3 years ago not a problem since!
Thought this was just something common to our bus and so was a little embarassed to ask about it ??? Tried cleaning our steering wheel with everything we had under the kitchen sink and nothing would stop it becoming sticky again within a few days so bought a cheap cover from ebay and solved the problem that way ;D By the way ours is a '78 so that fits in with the later steering wheels being made different??
FiftySixDelux do a wrap for 17'' steering wheels. I got one for mine when my wheel started wearing away. http://www.fiftysixdelux.com/restocal.htm
