Over the Christmas period I will be replacing the heater core (denso) on the wife's Golf.
If I flush the system before replacing the core, am I not moving the issue somewhere else? I will totally drain the coolant and replace with G12 evo but I'm sceptical about causing issues to thermostats and egr coolers by using acid to clean it. There is no sign of oil in the coolant, just the faulty heater core.
If I don't use the flush kit and just replace the core, how long before I'd see any problems further down the line do you think?
The had a new reservoir and lid in the summer btw.

Darren