I had same problem, at first I could not find out how to seperate the small silver cover with the on/off switch from the rest. After removing the 3 torx screws, 1 at the power entrance, and 2 under the shaver blade. You can remove the black cover. I also removed 2 more torx screws to separate the battery, from the rest, (don't know if thats really necessary). The silver covers are 'clicked' into eachother. When lifted the part where the battery part was screwed into, the silver parts became partly seperated, then you can pull the part apart.
I cleaned/washed the trimmer part with wd40 contact spray.
Assembled the parts, and made sure that the little plastic nodge was came into the trimmer.
Cleaned it all (removed leaking wd 40) and works fine again.
Hopefully this is helpfull to anyone.