Ok, you are on the better end of the spectrum.... the engine stopping by itself due to oil starvation being the worst case....
I suggest you find out exactly which bore your noise is coming from.... this involves a stethescope or getting lucky when taking the fuel from each cylinder one at a time... but only one at a time... see if you have a big difference in the noise it is making when it is making power compared to not...

It might be possible to just replace the lower rod bearing if you are lucky.... this would be sorta temporary... but for MB's that might mean 100 K.... they are very hardy as long as they have proper clean oil....
Main thing is finding out if it is rod/piston pin noise or rod /crank noise...