I repaired a wheel by filling the cracks with epoxy putty and then blending in different colour enamel paints to match the marbled effect on the Bakelite rim.
I seem to remember that it was in one of those 'blister' packs. You pop it through the foil and mix it up well between finger and thumb to activate the hardener. Probably got it from a pound shop. Then rubbed it down with fine wire wool,wiped down and sprayed with satin black. Didn't have fancy graining in the Bakelite on mine.
If you search for VW steering wheel restoration you will find a lot of info on how they do it. You can fill cracks with a colour matched plastic (search the wardrobe for a coathanger)