I can't answer the control arm/oil filter interference question, but regarding your original question, I've looked everywhere I can think of to look, and I can't find any reference to what seals those two pieces. I guess a call (or better, a trip) to a dealer to talk with an old tech that worked on the 2.4L engine when it was new-ish is in order...
Also, please be sure to come back to this thread and update it when you do figure it out so that other 2.4L owners in the future may benefit.