1 million miles???? yes it'll be ok until then because it won't have anything left to move water through.
I'd replace it, it's pretty easy to do on a duratec and not too expensive.
98.5 SVT
91 Escort GT (almost sold)
96 ATX Zetec (i brake to watch you swerve)
FS: SVT rear sway bar
WTB: Very cheap beater
CEG Dragon Run - October 13-15