Doesn't HAVE to be done but at 400+ it'll be dying sooner than later, some last weeks, some last a year.
Especially on ethanol.
Ask Joe what he reckons, he did mine. Mine lasted 2 weeks at 428 before 2-3 started slipping. But I was always getting it built anyway.
Joe said mine didn't look too bad when they opened it up though so I might have just been a bit paranoid and impatient.