use RTV sealant to seal the timing cover. you'll also want to see if there is a paper gasket available for your model.
run a bead of RTV aroung the mating surface of the timing cover, spead the RTV so that the entire surface is coated (don't spread it too thin. too much isn't good either).
do the same to the other mating surface on the block and place the paper gasket on one side or the other (the RTV should hold the paper in place).
carefully (so you don't shift the gasket) re-install the timing cover and torque to specs.
be sure you don't go too crazy with the RTV. you don't want to have bits of cured RTV floating around inside your engine where they could block oil journals.
'94 W124.036 249/040 leder; 8.25x17 EvoIIs
'93 W124.036 199/040 leder; 8.25x17 EvoIIs, up in flames...LITERALLY!
'93 W124.036 481/040 leder; euro delivery; 8.25x17 EvoIIs
'88 R107.048 441/409 leder; Euro lights
'87 W201.034 199/040 leder; Euro lights; EvoII brakes; 8x16 EvoIs - soon: 500E rear brakes
'70 R113.044 050/526; factory alloys; Euro lights