Thanks for all the responses.
I finally managed to get JL Audio support on the phone and spoke with Randy Wagner whom I can not recommend enough. He gave me some very detailed instructions about setup and calibration that I am going to run through...so if that doesn’t work, he said they have an out of warranty program where you pay $300 and shipping one way, and they will upgrade and replace any defective parts, no limit, until the unit is functioning as the latest model.
So I’m going to try the tuning and see if maybe I can get the same bass levels (or better) with less work from the sub, and if not, maybe send it in.
Thanks again.
(AND: I feel like a complete idiot because it's actually a JL F112, not a F110)