Mercedes 460

first af all you did not inspected cyl. heads before you install. check the surface and resurface heads if you sugest they are bad.

may be you damaged one of gaskets. It is really easy.

Are you sure cyl. block surface is clean?

And overtorqued cyl head bolt may damage head ore block in thread area.

 

with mercedes it is not so easy. especially on EU trucks.

well, there is wiring harness secured on front end of oil pan. unscrew this wiring box and keep it on engine.

Anyway I dit it in a hour. For me it is not a big problem to drop oil pan. But do not forget to separate oil level sensor connector))) LOL

 

Inspect head surface here