if mag starts out fine then slowly drops out most likely the center etac is dirty or just needs to be replaced. wipe off with lint free rag run 951 again,trc lin, engine check,system check.
There's a couple temporary fixes -
toner concentration adjustment
purge and replenish the magenta developer media
the techs will try these first to avoid the expensive and timeconsuming job of rebuilding the magenta developer housing