Well further to my May 12 post above re my '97 I now have to report failure of the black plastic OEM wp on my '98 at 62,000 miles on May 31.
This time 55% of impeller was still wrapped around shaft although not turning due to crack. Three other pieces totalling 40% retrieved, 5% missing. Cone was again OK, with minor scuff marks.
New metal impeller Tredex(GMB) pump now installed.

1998 Mercury Mystique Ls v6
VIN 1MELM66L1WK616503


98 Mystique LS v6 atx 110,000km
97 Contour LX v6 atx 125,000km
stock CD on LS, cass on LX
spoiler, tinted windows on LS only
4 wheel discs on LX only
All other available options on both