[Richard]

After multiple attempts, tools, and head scratching the recalcitrant cartridge is removed and replaced. In the end I used channel lock filter pliers. Not quite bit enough to span the diameter so I had to use hand grip pressure on the pliers to indent the cartridge before I started twisting.

I raised the coach as far up as possbile and cribbed it double. The only way I could get the necessary leverage was to stick my upper body in the tag wheel well. My arms were doing the Elvis when I finished.

A great big strap wrench was useless. It just slipped on the fliter. In hindsight I may have been able to stick some of those no slp treads to the filter, but that was just a thought.