That's some serious toy opening procrastination right there.

The good news is that the wheels on Ginrai and PM Optimus Prime are identical, so if you can find a PM Prime w/ a good condition wheel, then you ought to be able to salvage it. I actually had a spare junker PM Prime a few years ago, but nobody wanted it and I ended up giving it away for free to someone. Anyway, finding a spare PM Optimus Prime cab ought to be easier/cheaper than finding a spare Ginrai... there are some parts between those toys that are different, but luckily for you the wheels is not one of them.

Good luck.