Had this happen in a 1986 190D2.5 (602.911) a few years ago. Never did learn what caused it. Only 160K miles, always syn. oil, MB coolant. It neatly punched out the MB star cast into the side of the block trying to hide its manufacture
as "they don't do that". Still would like to know if a head gasket went south or another part of the injection chamber broke off. Had holes in the cylinder, beat up top of the piston, 2 holes punched out of the block (#4 and 5 locations), plus connecting rods that I didn't know could bend like that. Valves are fine, so were the injectors. It could have injested something, but who knows. So far, have put 100K on a junkyard engine we installed with no known history. Would install another if needed.