I am in the middle of a wheel resto right now. My wheel had pretty large cracks too. Here is what I did for what it is worth. I purchased 2 part epoxy, opened up the gaps enough to allow easy pouring, clean hub and the inside surface of the plastic with brake cleaner. Then I put masking tape over the bottoms of all the big cracks. Next I poured them full of the mixed epoxy and clamped them as close as possible to the original position. They actually closed up a lot. To be sure it would hold I let the wheel sit for almost 3 months (deer season). Then I filled the remaining cracks and gaps with 2 part epoxy putty from POR. After that hardened it was ground as smooth as possible with an angle grinder and 100 grit disks. I shot a nice thick coat of primer filler next. Last night I put the first coat of premium quality filler and will sand tonight and apply a touch up coat to any areas that need it. Pretty tedious work but the reward is worth it. I will post up pictures once its all done.