4.2tdi

[ainarssems]

Brake fluid - change every 2 years on any car
Coolant - not sure on 4.2TDI but it ranges from 2 years to lifetime, usually 2 years are for high performance engines with higher thermal stresses. If it's drained for some reason it usually gets filled with new coolant.
Thermostat - Normally changed when it's either faulty or if you are doing other work near it and it makes sense to combine jobs and do it at the same time as preventative. I think it's not too bad to change it in 4.2TDI.