the collection of the brown paste behind the block plug that is leaking is someone years back replaced the OEM antifreeze with the stuff we use to have in the USA that is not compatible with alloy headed motors - and the water they put in with it is loaded with iron - we have always used distilled water ( stuff used in an Iron ) is the only water allowed in an alloy blocks - headed motors -

ALSO their is a picture that to me shows a slight head gasket seep - its the #6 cylinder on the exhaust side towards the front of the motor looking at it 7 o'clock - its looks as if some kind of fluid combustion transfer was going on -

at first when I read this I was not sure of the mileage but after seeing the engines inside condition shown in pictures it looks about right oil changes were done on time or before , as far as cleaning out the cooling system I would not put any of the caustic stuff they sell for that purpose, I would fill it with water only and every day for 2 or 3 days drain the block, take it to work and back ( block drain plug is on the side close to the leaking plug on the earlier car don't know about yours ) and flush out the rad then I would put in the pento stuff I like the blue and swap it out every 30,000 miles - the red is forever well nothing is forever - care must be taken not to get the little bits while cleaning into the cylinders and chain case area use PAPER towels not rags ( RAGS leave material lint every place they have been and you cant get it out of the very small places ) as far as the exhaust is concerned you cant powder them the fumes will choke you to death while its burning off ( forever ) - the only thing is by a company called Jet Hot in PA http://www.jet-hot.com/import.html ( they do drag car headers and it does not come off my guess $3oo or so to do the small MB manifolds looks as if you are on the path to getting it done good luck -- jz