I just went thru this NIGHTMARE with my 300SDL. Same problems you are having.
I torqued the pan down too much, feeling no resistance, and warped the pan, cut the gasket, and deformed the ears of it.
My mistake cost me about 5qts of ATF in front of my house on the street, a new $70 pan, $7 gasket and $10 in ATF.
Just torque the bolts evenly so the gasket makes good contact with the tranny itself. No need to go overboard here, as we both found out the hard way.