There were always problems with the drivetrain when trying to pull heavy loads.
It went up to 12kg total weight (transformer transport) but only with a crack.
Now I've used the new diffs and nothing cracks anymore, even with more weight.
The Actros weighs 2.9kg, the module 1.6kg, the shovel tooth 4.6kg, the large brick 2.7kg and the small 0.33kg, making a total weight of 14.6kg