The lower timing cover does not use a gasket, rather the special MB black sealant to seal the timing cover to block surface.
I'm not sure where you saw the inconclusive argument regarding whether to replace your 103 chain or not, but the majority of advice and experience of techs and DIY'ers, including myself, is that the chain does not need to be replaced, if you've been changing your oil regularly.
The typical failure of these chains is due to breakage of the timing chain guide (plastic) and/or tensioner rail. Over time, these parts get very brittle and can fail. So, "while you're in there", whether or not you replace your chain or not, it would be very wise to replace the chain guide, and tensioner rail with the timing cover off.
Also, it wouldn't be a bad idea to replace the crankshaft seal on the timing cover, as it's only a $6 part, and easy to replace.
Larry's advice about the top timing cover is right on. If you "roll over" the top cover U-seal gasket, it will leak, so be careful.
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi