Custom cooling won't start leaking accidently, you test it when you build it (EKWB even sells pressure device to do this more intensively) and if you tightened everything well, it will be quite leak-proof. The hardware is quite over-built.
Just for information, the custom loop is +/- 800 Euro.
The same cannot be said for All-In-One kits, which are generally poor quality and I would never personally go for them instead of air cooler. Noctua NH-D15 is just as strong (and often stronger) than most of these AIO kits anyway, it's just sadly not available yet. UH-14 is ok if you don't overclock.
The Thermaltake LiqTech series has proven itself worthy to be ignored (faulty over 4 revisions). Terrible quality control, too much risk.
And overclocking 2990WX is not really worth it, your single-core turbo is already capped (it will never go higher than 4.1 +/- GHz no matter what), so you can just rise all-core turbo and get additional 10perc. performance in exchange for more heat/noise. PBO makes this quite easy and is the correct way to do it (you can do manual all-core fixed ratios, but then you loose the single-core boost in exchange and that's much bigger benefit for workstation).