Hi frost it could be something as simple as your battery is so far gone
that there's just not enough power to do anything
and when the weight is off the wheels and off the gears it has just enough power to move the wheels
replacing the esc is your choice it means you also remove the servo connected to the msc and the heat sink
which lowers the over all weight
depending how far you want to take your bycmo with upgrades you could replace the old radio gear with a 2.4g it means that you can take your car anywhere without worrying about interference also means that if you change the bodyshell there's no need to drill out for the ariel