The green stuff is not good. It provides good corrosion protection, but the inorganic salts used for corrosion inhibition precipitate out a lot of deposits. Your aluminum radiator core won't corrode through. It will just clog up. Mercedes antifreeze is formulated with an organic inhibitor package that, according to my research, is very similar to Dexcool, and since Dexcool is available through the aftermarket at reasonable prices (Havoline Extended Life) I use it in all my cars. When replaceing green stuff with an organic inhibitor antifreeze the system should be thoroughly flushed to remove all traces of the green stuff.
After draining, thoroughly flush the system by cold flushing both ways through the heater inlet circuit through the nipple/hose at the back of the head. The drain valve at the lower end of the block on the exhaust side is reachable with a crescent wrench or socket. Lossen it, then attach about a 3/8" piece of hose to the nipple and route to a pan. Then hand turn the valve about one full turn until coolant starts to drain. Mercedes makes it very simple to drain the coolant on the inline sixes without making a mess. The radiator drain valve (behind the removeable cover on the valence panel) is also set up to accept a drain hose.
Once it's thoroughly cold flushed, fill it with water and operate the engine until the thermostat opens and a few minutes after that. Then drain, and if the effluent is colorless and tasteless, you're ready to install an organic inhibitor antifreeze. If not, repeat the process
It's not necessary to remove the thermostat.