If I open the cover of the ccv, as u said if the spring is saggy or the membrane is too hard then it needs replacement; right?
It appears like this one may be opened. Peugeot moved to favouring incorporated in the valve cover, and not 100% sure which type this is, just suspect it is one that can be opened. My for instance, is incorporated in 2013 and even earlier models of the 4007 but has oil decanter system as well.
Frequent regeneration of the dpf can dilute engine oil and it also cause too much consumption.
off the top of my head,
The DPF is after the engine, and I'm not sure how regeneration aides dilution of the engine oil. The system for DPF regeneration is largely passive on Peugeot. An additive is mixed with the fuel, which lowers the required regeneration temperature, which accumulates in the DPF. Then assuming the temperature is reached, and other burnable material present, it burns. There are certain materials which won't burn also collected, the additive packages contained in the engine oil (to name, is one source).
Engine oil dilution is usually from mixing with diesel fuel, this could be from a defective CCV, oil control rings, excessive blow-by (turbo or compression ring issue), problems with the diesel injectors. (not tried to cover every source, just likely ones, and this process is normal as well, why oil needs to be changed in any turbo diesel, more than naturally aspirated diesel)
If you have excessive oil entering the DPF, would be thinking about the turbo, this is usually how they die, dumping engine oil into the exhaust from the turbo bearing.
Diesel Smoke Diagnosis Guide - White, Grey, Black, Blue - learn diesels
DPF Regeneration Fluid (Eolys) in PSA Engines: A Guide for Professional Mechanics | JLM Lubricants
Hope you find this useful.
