<< I have an old shower that really need a cold cartridge/valve unit. >>
Bite the bullet and go for a whole new assembly. Over the years I've attempted
to civilize ancient pieces like this, some with moderate success, most with
early failures after repair.Your odds aren't very good and since you'll wind up
replacing it soon anyway, just do it over right the first time and move on to
more urgent matters. Kohler and Delta seem to me to be the easiest to retropfit
into older installations. Good luck.