Oil cap popping off!

Since long the engine has had a problem with the oil cap popping off, and as a result oil was spraying up and over the whole engine making a total mess.  I had been told that this is probably because the engine is worn and that compression is passing by worn piston rings and pressurizing the sump. I didn't quite buy that explaination as the engine starts and runs perfectly without any smoke whatsoever. My suspicion was that there was something wrong with the oil return system connected to the oil cap, that there was a blockage somewhere.

So first I tried to just disconnect the hose that's coming from the oil cap and re-routed it into an old oil can:

This solved the problem, so now I knew that the problem was indeed where I suspected.
The oil return/separator system looked like this:

I put a question to forum.landrovernet.com, and got some good tips. It turned out that top item in the picture above is not needed, so I removed it. I also found that because of this extra item (don't know what it is, my guess is a non-return valve) the top hose had a bad kink in it which I hadn't noticed before. After re-connecting it it looks like this:

After this I took a long drive which would normally make the cap pop of, but when I got back it was still on and no leakage along its edge either. Case closed :-)