Hi, just had a service on my 2.0 diesel octavia estate. On picking up the car they told me there was evidence the coolant was contaminated, and would need flushing and replacing, along with the expansion chamber. The time they allocated to complete this was 6 (yes six) hours and said it will cost £850. To me this seems very excessive. Is this the garage trying to claw back lost revenue? or is this legit? Would be grateful for some guidance please.