I question grinding out the cracks so large only to fill them back in with a thick putty. That's a lot of extra work to file and sand smooth. I prefer to apply a medium viscosity epoxy, like JB Weld, into the smaller cracks. As long as the epoxy fills the cracks it works very well. Open up the cracks only wide enough, like with a hacksaw blade, to allow the epoxy to squeeze in.
Steering wheels can certainly crack again in the future, just like they cracked in the past. After all, they're designed to be flexible for crash protection - plastic over a steel hoop. They're subject to driver use and abuse, hot and cold, sunlight and general aging. I think it's more a result of use and care, not a certain epoxy.
Gord, what is your steering wheel repair guy's technique? I agree an automotive epoxy paint would be superior. Can you give us an Ivory color code?
Happy New Year everyone!!