I’m sorry JSM! I read this post yesterday not long after you posted it, and I THOUGHT I had responded. I click back on today and I guess I never did. Bunnytowne said what I was going to post. I wonder if it’s a urinary tract infection. And Like MooBunnay said: It’s not normal for him to be wet like that.
His diet sounds less than ideal. The grass hay is good, that should be the main part of his diet! The cereal mix concerns me. Are those “gourmet” pellets with colored bits, seeds, corn, cereal, etc… If so, you may want to start transitioning him to a plain timothy pellet. You can begin to make the switch by picking out all the bits that are not plain pellets, and then transition him onto a food that is already plain timothy. Sunflower seeds are not necessary in his diet either. They’re very high in fat. Being overweight can cause all kinds of issues for a bunny too. Is he on the chunky side? What veggies have you offered him that he does not like?