The last 2 thermostats I replaced. '83 300D, '84 300CD both came apart while I was removing them. Quite a bit of scale around them. I took 2 screwdrivers, put one through the thermostat and the other put the handle in the outlet tube for the housing. You sould be able to force the thermostat out.

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'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.