My alternator shook apart a few weeks ago so I took the bracket off the side of the motor to be wielded and bent back the other night. As soon as I got it off a good cup full of sludge fell on the ground and the back of the bracket was filled with it. After blasting it with brake cleaner I found a 10mm hole in the side of the block, it was a smooth bore so I'm guessing mercedes put it there. Any ideas why it's there and is it ok for me to seal it?

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84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800