You say Mayhems fluid has a maximum lifespan of 3 years. What is the problem with using it for longer? Is it that it cant transfer the heat as well? That is clogs up blocks etc?
If it is heat related have you tested say... 4 or 5 year old fluid against new fluid?
I only ask as I know someone who bought a pre-built watercooled PC with blue fluid about 6 years ago and it still has the same fluid in it. His temperatures don't seem that bad to be honest. I did clean his blocks for him a year or so ago as they were a bit gunged up however. I didn't know how old the fluid was at the time otherwise I would have recommended that he replaces it at the same time.
Inhibitors lose there effectiveness after about 1 to 2 years how ever the Nano fluids prolong the life as they block out light and this help in the longevity of the fluids. We say 3 years max as that is our test time as in we have physically has it in a fully running system now for 3 years with no issue what so ever. So we can state this as a true fact not just some made up figure.
Aurora contains nothing that can harm the environment pastel contains Zn0 which can.