I ended up with a very slight coolant leak on my old 2011 Audi S4, it was on an alloy coolant pipe stub/cover, which Audi later changed to being plastic, it would have been me that caused that very slight leak in the first place when I replaced both the front drive belts, the front had to be put into the service position to create almost enough room to do that job - so that meant the large coolant hose that connects the top of the engine to the RHS bottom of the radiator ended up getting flexed, and that was enough to crack accumulated dried already leaking out but resealed coolant. Now maybe cross posting or going off track a bit here - this alloy pipe stub would have always have been doomed to leak, as with many other areas in VW Group cars, where you have an upwards facing open end of a pipe fitting, road salt or salty water from same gets thrown in and "does its business, in that case, causing slight surface corrosion down and across the face of the O-ring seal in that "quick fit" coolant pipe coupling - same as on the TB on my wife's 2015 1.2TSI VW Polo where it causes an oil leak even after cleaning the alloy TB charge pipe stub and replacing the O-ring! Back on track!
That leads me onto one suggestion, to avoid the possibility of a future leak at that RHS lower radiator "quick fit" coupling, I'd always replace any rubber O-rings fitted to these removed "quick fit" pipe couplings - Audi workshop manual mandated that as I'd think all other VW Group marques would as well. I found these "quick fit" pipe couplings can be quite difficult to refit especially after replacing the rubber O-rings.
I bought and used a Draper Coolant Vacuum Refill Kit, you need a small compressor to operate it, but it did a very quick job on my old 2011 Audi S4 - though car has a very high engine and heater pipes, so it really did
help minimise trapped air. One other suggestion for anyone opening up their cooling system on a "more modern" engine, aim to collect and so measure the actual volume of coolant removed as by doing that you will be able to gauge a lot better when you have enough coolant back in the system to run the engine without causing some areas to get too hot, maybe not on this engine, but most newish VW Group engines, there are common but almost isolated sections in the cooling system - so just dumping back in coolant at ambient pressure might not work too well - and that is where the vacuum refill kit comes in handy as does venting where advised by the workshop manual and even running any electric coolant pumps, the "charge cooler" system is normally almost isolated and has its own electric pump on most engines.
I just replaced the coolant with G12evo due to the coolant in my car being over 10 years old and G13's base coolant concentrate does not seems to be the best ever coolant that BASF produced judging by some later models needing additional Silicate dosing pouches before VW Group (and BASF) moved onto G12evo - just my thoughts, that is all.
