Update:
So, I decided to tighten the oil filter cap with an extra 5Nm on top of the 25Nm. I started the engine and after ten minutes I again noticed the usual very little oil leak that I was bragging about these last days on this very helpful forum. So then I decided that 30Nm won t do the job either. It happened that some time ago I had bought an oil filter kit from a site called comline auto parts, if you google it you will find it immediately. I decided to take the filter cap off once again and replace the large bosch oil seal with the seal that came with the oil filter kit from comline auto parts. Again, I started the engine, after 10 minutes I found no leaks whatsoever. I then went to test drive it and this time I made sure to make 20 miles instead of 15 miles like I did before. Once back home I checked for leaks and thanks God I found none. I hope I have solved the problem once and for all but two questions keep lingering in my mind. One, did I really solve the leakage problem or would it happen again on my next drive (as I explained in the posts before)? And two, if no leaks will happen, how could a seal from comline do the job and a bosch seal fail like this?