First off, congrats for having such a wonderful older bunny! He sounds wonderful, and very spoiled, which is as it should be. :biggrin:
One thing I will suggest, if your bunny is now having difficulty with a litter box due to health concerns, is purchasing some vet bedding for the floor of his condo. It's highly durable, washable, rabbit resistant, and is designed to keep animals safe and dry. The urine is wicked away from the matting and the top of the bedding remains dry, which in turn keeps bunny's feet/body from getting damp. I used it when I had a rabbit who became completely disabled, and it was the best thing I ever invested in for him, as it kept him not only dry and clean, but it protected his body from developing sores as a result of lying down. I now use vet bedding for my rabbit Yofi, who is prone to sore hocks...and ever since I put it in his cage, his sore hocks haven't returned.
If you ever do get some, see if you can also get something to put under it to help absorb the urine a bit (I currently use a mat that was designed for outdoor barbeques; also washable). The only drawback is having to change the bedding and do more washes, but it's definitely worth it.
Oh, and do you have any pictures of your bunny? Would love to see him! :biggrin: