Should be on on passenger side of block
I don't think Benz has changed their location for the block heater plug, it should still be on the passenger side of block under the intake manifold about center. I would however purchase a new intake/exhaust gasket before attempting removal of this plug. Chances are good that you'll have to remove the manifold to get the leverage and clearance needed to break the plug loose. I don't think it's just going to come right out with ease. Many have posted the use of three or four foot cheater bars to get it to budge. The only fluid that might run out is a bit of antifreeze seeing as the plug is threaded into your engines water jacket. As far as torquing the block heater, that one I can't answer as the fitting on the heater would require either a crows foot or an extremely large socket to torque it down. I'd prefer to use a cresent wrench with maximum arm torque to secure it in place.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan