Actually, @Theron's response makes the most sense, so I'll try that first. Thanks!
It hasn't been an issue of not getting the old one off - I have wrenches for that. It's more about it not being that "glued on" in the first place. I always thought that smearing the O-ring with oil (new or old) should keep it from sticking later on - guess not.
@ALB - It mounts to the inside of the frame, inboard of the wheel well, with a piece of 3" X 3" Angle stock. That used to be aluminum but it got torn apart on the last filter replacement so I replaced the aluminum angle with a piece of 3/16" 3" X 3" steel. THAT should handle it! Everything - Filter, MOCAL sandwich, fan switch, etc, is inboard of the wheel well for protection.