I have a few watches that I do my own maintenance of. What I notice is that as oring aged, it become weaker thus too water that is too hot will make it weaker.
Also another point is to never put oring in a freezer for too long (for those of you with stuck atty) rubber become brittle when cold.
Depends on whether the oring is silicon or rubber. Rubber oring are easier to degrade.
I clean rubber/silicon oring will warm water (35 degree Celsius those type) and mild neutral soap.
For metal and Pyrex, you can go ahead and soak in hot water.
Any kind of plastic tank, be careful, wash off with mild soap and never use hot water.