Re the M104 question , I have had numerous cars with M104 , and M103 which is virtually the same engine , and lots of other straight six Mercs , most of which have been well beyond 200K ( my 300-24 reached 430K on its second engine , 380 on the original not all in my hands but it came with detailed history ) and I've never changed a CHG on any of my cars . A couple of them have had slight oil sweats from the bottom of the camboxes which I lived with ; had a couple of water pumps go along the way but no other coolant losses .
I wouldn't worry about your engine therefore .
Did once have CHG go on an Audi 100 some years ago in spectacular fashion with clouds of steam out of the exhaust , but never on a Merc .