[3dem] Clip ring question

[Eduardo Sanz Garcia]

It seems to me that my clip ring doesn't lock the sample as well as my 
cryo holder used to do it. I have some times the impression that the 
clip ring is lose.
Two month ago, or so, when I inserted the clip ring it made two 
notorious "clicks". Now, I am not able to hear that sound.
Is there any problem with that?
I see the potential problem that the temperature is not transmitted 
effectively between the holder and the sample if the clip ring doesn't 
lock well. Is this a real concern?
Do the clip rings need some maintenance (plasma cleaning...)?

Thank you very much.