I have my 2004 400ex forsale. The whole motor and transmission were just rebuilt and It has about 10hours on it since that. The plastics are rough but I assure you that it runs like a creampuff and the tranny shifts perfect.
It has some aftermarket parts on it like:
Renthal handle bars
Moose clutch lever and perch
pro armor killswitch
Whitebros e series full system
LSR bearing carrier
Moose slotted rear rotor
Reworked rear shock with an Eibach spring.
Brand new OURY grips
* the choke has been removed from the carburator. But it starts fine with a few pumps of the throttle*