2.0 TDI Sealing Kit for PDE Fuel Injector Lines

Hello, I've been searching online for a while now, but so far without success.
My A4 2.0 TDI (16V, made in Germany) has been increasingly leaking oil for the past two years. In addition to a spot near the valve cover gasket, it seems that the area around the entry point for the PDE fuel line is also oily. Apart from things like a tandem pump, I can rule out almost everything, but the area is very difficult to access and inspect.
I once read somewhere that the gasket in the introduction might be leaky, or possibly the introduction itself (but I can't find that information anymore).
In the Pseudo-AKTE 7Zap software, only the wiring harness for the 8V engine (without glow plug wires, with flange) is shown. And there is no individual gasket included. For the 16V engine, I only found a copied overview image, and even there, no gasket was shown. In pictures of new parts, I can see an O-ring in that location. Is it possible that this O-ring is not sold separately? Surely, many people must be experiencing this problem?
Therefore, my questions are:
- Is it true that there's often a weak point here?
- Is it definitely an O-ring?
- Does anyone know the dimensions (of a 16V engine)?
- or, if possible, the part number, in case it's available as a single item.
available?
- Or could the problem not be about the introduction itself, but rather lie within the way it's being introduced?
I could certainly expand it and measure it, but then the car would have to sit for a few days while it's delivered and installed.
Who has relevant experience with this specific vulnerability?
Thank you.
Andreas.