Re: Samsung PCJ612R crt coolant change
$600 is absurd.
If you choose to DIY, get a service manual and be very careful. You will need to do alignment including convergence.
I would look for another servicer who will do it at a reasonable rate.
Typically, the blue and maybe the green need coolant changes. The red rarely, if ever needs it. It is useful to leave one CRT alone anyway to have a reference for alignment when done.
Looking for me, just google my username. I have used the same one for most sites for many years.