I would safe money to buy new servos and radio. ...... perhaps futaba or ko propo.
I would suggest you to buy metal gear servos with speed around 0.10 sec to 0.13 sec , and 13kg of torque.
I have lots of mtx3 parts, ...... you can PM me if you need mtx3 parts. Some people in this forum also have mtx3 parts too.
Some MTX4 parts are useable in mtx3 : gears, pulleys, cvd, clutch shoes, etc.
Dont worry about spare parts. Enjoy this hobby and follow the racing line.
Another suggestions : use longer screws 3x12mm to strengthen the whole car.
On Road : Xray NT1 , RX8 , T4 || Mugen Seiki MRX4-R , MTX4 , MTX3 prospec || Tamiya M03 , M04 || Top Racing Sabre FD2
Off Road : Xray XT8 || Hobao Hyper 8
Radio : Futaba 3PKS || KO propo EX-10 eurus