i thought the same thing when i was putting my m103 together, and on all three m104 and and two 16v engines ive taken apart, there has been no sealant on the rear main seal flange. Just by looking at it, it would appear that the only spot oil can get out is at the bottom, and the oilpan gasket covers that

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1993 2.6 (040) SportLinE 5-speed - Armed to the teeth w. roof rack/2x bike carriers/8x ski carriers/MB towing bumper
1993 2.6 (040) - deceased/reincarnated as a trailer.
1987 16v (702) - Now parting out(9/22/10)!!! - Email me your requests for 16v parts- Engine and full body kit avail!!
1987 300SDL (122)- For sale!