Did not imply your piston rings are gone, just letting more combustion gas through (increased compression & temperature due to remap?).
A stuck valve would have much more noticeable consequences I'd think. Carbon deposits on valve seat(s) possibly, but not with that sort of mileage.
The breather valve or PCV (marked "TOP") limits the depression the turbo applies on the breather hose as engine speed increases. You can check how much direct crankcase blow-by you are getting by lifting the oil dipstick while idling. If no blow-by then is either the valves or a faulty PCV. But I'd say it comes from below.
Blow-by is completely normal on a modern diesel engine, but is IME aggravated in the Td5 due to the poorly designed oil mist recovery system (crankcase gas 'swirling' chambers within the rocker cover that supposedly condense oil which falls back into the cylinder head). Thence the recommendation to install a proper oil recovery system.
Also the air filtration system is not a very bright one for pure off-road use as engines tend to get "dusted up" fairly quickly contributing to increased blow-by.