You don’t have to disinfect his area more than you normally do when you clean it.
Sticky poop or poopy butt is common in rabbits and it’s unformed cecals that not get eaten. It is a disturbance of the gut microbiota, but generally not a serious one and the remedy is normally more hay (=fiber) and less pellets. Sometimes it’s a certain green the bunny doesn’t tolerate. (I f ex have a bun that gets poopy butt from carrots.) There is no patent “cure” for this, you more or less have to do elimination experiments to try and get it right. Here is an informative article from the House Rabbit Society (trusted source) on this subject: http://rabbit.org/intermittent-soft-cecotropes-in-rabbits/
Our gut microbiota and that of our pets change with age and so do our nutritional requirements and ability to digest the food we eat. In general, the ability to digest and and absorb nutrients becomes less efficient as we age. Sometimes a probiotic like Benebac can be of help.
Any GI-disturbance in a bunny is, as you seem well aware of, an observandum, so keep an eye on appetite and poop – in case he stops eating/pooping, you should contact a vet.