Do I have to use a factory oil filter in my [DSM]?

No, you don't. It is true that the original Mitsu/Chryco oil filters have a small check valve in them. The common belief is that this check valve helps maintain oil pressure, and keeps oil in the engine while the car isn't running. (Dealers often repeat this tidbit of DSM 'lore' in an effort to steer owners away from the popular oil-change companies.) Some suspect, however, that the valve is nothing more than a bypass valve that allows oil to circulate even if the oil filter becomes too clogged to operate properly.

In any event, the aftermarket oil filter manufacturers include the check valve in their own offerings for the DSM triplets. This makes perfect sense, as it is unlikely that either Mitsubishi or Chrysler manufacture their own oil filters. Those who prefer OEM parts may, of course, stick with what they are most comfortable with, but it is by no means mandatory.

Final Word: You should still stick with factory but do not need to.