You have a 1.8T ?
I would check the inlet manifold gasket for sealing effectiveness. Even though they may have fitted a new inlet manifold gasket the seal may not be getting sufficient clamping force due to either the manifold being warped or the bronze ferrules slipping in the manifold itself and no matter how hard you tighten the nuts the gasket will never be clamped with enough force for an effective seal.
Do you have:
Coolant level dropping but cant be seen where from?
Uneven idle when cold?
Super clean spark plugs on cylinder 1 and 4?
Vacumm leak?
Have a look here on a fix.
https://the75andztclub.co.uk/forum/s...Inlet+manifold
The best long term solution is to fit a VVC alloy inlet manifold and mounting bracket.
If you have eliminated the leak then when you fill up use this simple no cost reliable procedure to bleed the system.
https://the75andztclub.co.uk/forum/s...light=Bleeding