Andy, another way to assist the sticking clutch scenerio is to use fine shaved graphite dust, its easy to obtain from any lead pencil
the advantage here in using the graphite dust is its a dry form of lubrication and works great for certain metal part components such as the E-starter clutch assembly. I personally never use any liquid based lubes on the starter clutch mechanism as the centrifical load always tends to eventually send liquid lubes ie oil, WD-40 etc where you did not intend like the clutch O ring, even if only a small amount is used. Give the graphite dust a try and see if that helps.....

Cheers- Marty