The best thing for nitro cars is patience, as suggested by previous replies if it's ruining well with some smoke and it's not bogging down then just enjoy playing with it while it lasts haha. most nitro cars will need a little tweeking from day to day as different weather conditions mean the ambient air could be thinner or heavier on humid days meaning they may need leaning or richening up a little in accordance. Most bashers find a happy medium and that'll do kinda thing where as racers need peak performance for each race.
I have a savage x with a 5.9 lump in it and a lot of people say they're hard work, but once id sorted any little issues out it's ran like a trooper for months now without feeling the need to re tune it and I've been out through summer and winter all the same.
Sounds like the one way bearing has gone as that is what grips the backplate shaft and turns your engine over, take it out and have a look to see if its cracked, if not then you can either replace with a new one or try and clean the gunk from that with cotton buds and put it back on the shaft and see if it grips. If it does then winner, if not then it's a new one I'm afraid. I've been through quite a few too....