most blown 4n1's result in consistent control problems, not randomly. regardless, my first guess would be a glitching 4n1. so you probably are right, you would need to replace the 4n1. you can save some $$$ by buying a 3n1 instead, and using the reciever from your 4n1. there are no real modification to do this. it's pretty much plug-n-play; you just need 2 servo extention wires, some double sided tape, and if you want to get fancy, some shrink wrap.