Often refered to as the hollow bolt. there is a crush ring that goes under the head of that bolt. sounds like you need a new one. I think this is it. there are also two rubber o rings that go towards the other end of the bolt. might as well replace them too. And since you'll have the primary filter off, well... And well, good time to replace the clear filter too


http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=22H17A47H24L0Y2IQC&year=1979&make=MB&model=300-D-002&category=Y&part=Seal+Ring

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=22H17A47H24L0Y2IQC&year=1979&make=MB&model=300-D-002&category=E&part=Hollow+Bolt+Seal+Ring

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86 190D N/A 2.5L Auto 265k "Ruby" -Sold-
79 300D 242k "Condi" my first -sold- RIP
2013 chevy sonic hatchback - had to for work