You might want to inspect the head bolts. those are a strech shank style and have a max allowable length.
If the heads have been on/off more than twice, you will need
new head bolts.
The torque sequence is :
stage 1 55nm
stage 2 90deg angle of rotation.
stage 3 wait 10 minutes
stage 4 90deg angle of rotation.
There is a specific pattern to torquing the bolts.
Start from the middle and work outwards alterntaing sides
as you go.
P.S. A very thin wipe of loctite 5900 sealant from your MB center
applied to both sides of the headgasket around each oil pressure galley and drain return can do wonders.