I have a similar issue with my Silvia.
About 2 months ago whilst replacing the steam wand (cos I scratched the original) I had the lid off. I noticed a little piece on the inside of the steam valve assembly that looked to have slipped a little. I slid it back into place. Seemed to help at the time.
It still does not always close 100% (I often have to give it an extra tweak) , but it seems better than it was.
With regard to its turning, I never have to use much force to turn it on or off, but it does sound somewhat squeaky. Mine is about 2 years old.