sorry, but the nature of toy grade is break and replace. you wont find much with replacement parts available. that said, 4 years old isnt too early to get started in hobby grade rc. yes, there is a significant price difference but you will save money in the long run. here is one that looks about perfect http://www.modelsport.co.uk/kyosho-s...roducts/387720 i am totally aware that this is literally 3.5 times the price of the vehicle you previously purchased your son, and it does not have tank-style steering. however, it does have readily available parts and it can be upgraded to go faster when he gets older.