How old is this brick?
It looks like part of the old 9-Volt motor that was made from 1990 and 2002.

The full thing's part number is listed as 2838 which I assume is the mold ID stamped on dark grey base, while 2837 is the mold ID of the top part.
I don't think it's supposed to come apart, it looks like there are 4 clips on each sides which have been broken off of your piece.