Recently I was doing research on the MGA cars of the 50's, when I came on a blog that had a question on how to repair a cracked original MGA steering wheel. There were several excellent descriptions on how to do a complete repair.
Most suggestions followed along the lines of using various "fillers" such as epoxy glues, epoxy putty, "bond" like material and even a special fill product sold by Eastwood (which is an excellent product). After filling cracks and missing areas, you need to sand the repaired areas. This is a tedious job and will probably require more than one fill coat and multiple sanding sessions to get the wheel ready for final paint.
This does work and will make a nice repair. Most likely, it will need to be redone in a couple of seasons. Why will this repair need to be redone? For that matter, why did the steering wheel crack in the first place? The answer is simple. Most early steering wheels were made by forming the shape from metal shape or rings and then covering with plastics. The early plastics were thermo reactive plastics. Basically, the plastics expanded and contract at a faster rate that the steel frames. Thus, the plastic cracked. These cracks enlarged and chunks fell out, leaving a real mess.
Today's fillers are much better and resist thermoplastic cracks. But, if you are using these with the original "plastics", you will have cracks at the union at some time. Instead of this type of repair patching, why not install a high quality leather steering wheel cover on your special car. A good fitting leather cover will hide cracks and even cover some minor lost chinks in the plastic. You will save a lot of time and you should never have to do it again. An excellent choice is a custom fitted Wheelskins cover for your wheel.