I can't offer any ideas, only sympathy.

Couple weeks back, I did a renovation here which involved moving the litter boxes down cellar. Two cats started using an upholstered chair or the sofa. I phoned upholstery cleaners, who advised me there is no way they can remove the stink of cat urine. I then tried re-upholsterers, but they couldn't fix a La Z Boy recliner seat base. So I had to throw out the chair. The sofa had a slip cover on it which protected the cushions, and I ran out and bought a vynil backed mattress pad to put under the slip cover.

Once the reno was done, I put one litterbox back where all 8 used to be (left all the others down cellar) and now everyone is happy.

You mentioned that you are moving, and I wondered is this has upset Clyde at all, making things worse?

He is a wonderful gray boy, love the photos!

Cover the seat base with plastic to protect it from additional damage, beyohnd that I have no helpful tips.