This is done on engines fitted with timing belts in which the seal is fitted in the front of the oil pump body rather than the engine front cover except on GLC and 1979-82 626 models. Start by disassembling the timing belt covers, timing belt and timing belt crankshaft pulley. Very carefully peel off the seal of the front cover with a small prytool, but make sure not to damage the bore of the oil pump housing. Completely wipe away the seal bore, and any dirt or grease may cause the new oil seal to fail too soon. To fit, smear the lip of the new seal with engine oil and fit a piece of pipe, or a socket, which is a little smaller than the bore of the oil pump, to tap the new seal into position, the front of the seal lining the front of the oil pump body. Lastly, reconnect timing belt crankshaft pulley, timing belt and timing belt covers in that order of their removal.