What you are describing is definitely not typical (to the point where most of what you are saying are problems we have never heard of before). The wheel adapter holes should be approximately 4.1 mm in diameter (I just measured one here myself to confirm). Can you post a picture showing how you are measuring the shaft adapter holes? Pictures or video showing the off-axis tilt or wobbling would also be helpful.
Similarly, the motors should be very tight in their brackets; I have tried removing them before and it was not easy to do so. If it did spin freely when torque was applied, then it sounds like Dagu might have neglected to appropriately tighten the bracket screws; can you check if this is the case? If you email us with your order information, we might be able to send you some replacement motor and bracket assemblies.
By the way, stalling DC motors like those on the Wild Thumper can dramatically decrease their lifetimes and even lead to instant failure, so I am concerned by your statement of “if a wheel is blocked for a while…”. Whether the brackets are appropriately tightened or not, you should avoid stalling the motors for even short durations, let alone “a while”. It is possible this is why one of your motors is drawing so much more current than the others now.