Looks to me as if the prior owner never cleaned them. As for changing the orange bellow you just need to remove the nut and washer that holds the bellow on. Seafoam and carb cleaner mix and a copper wire brush and clean them shiny. I'm running Amzoil interceptor in my 900 and my valves don't look anything like yours. Them look sticky!! Good luck and have fun.
With that much gunk in there I would pull the cylinders and do a thurough cleaning on the ports for the valves and also that way you don't have anything end up in your motor.