My experiences with solenoids can be summarized as follows:
...when they start sticking, replace them.
...if they start stinkin, same deal.
...if the stinkin' solenoids are sticking, they might start stinkin' soon too!
...it gets sticky if they stickin' solenoid gets funky, then replaceing them can be a funky stinky business dealing with stinkin' solenoids.
...who designed this stinkin' thing anyway!!
_-_-WBear2GCR