more of s400 problems can be discuss here
Serpent to 1/10th EP Touring Kit S400
as for parts, ther r lists of compatible parts can be found at above link too...
1) check EPA setting.
2) if u r running very tide wheel width then maybe the cvd n the spool outdrives might not have enough tolorence hence bearking either the cvd or the outdrives
3) it's very usual that it chatter a bit (most spools do the same), ETS/DUJ/Losi solve most of it... ther's a SPEC R unit that fit 416 can fit into S400 too... i haven't got time to try that out yet...