I had the same problem with that little o-ring seal for the filter, it just refused to come out, it was seized pretty well, so I had no choice but to use the old one as you did, by the time it is due for another change I'll try a little harder to remove the old one.

On my 05 leabre when 1st started and cold it was real slow to go into gear it had 187k on trans. so did trans service and changed filter when i put in new filter I didnt replace filter seal and put in new filter it slipped in real easy. then got to thinking may be it was not sealing and was sucking air so pulled old seal out and installed new sealand lubed up and then had to use hammer to tap filter in to place and now it has no more delay going into gear and put on about 4k miles and still doing good

That little seal is okay to leave in there. I hear it likes to get stuck more than it likes to wear out. Glad to hear your car is giving you less bullshift and more performance shift.