'91 Jeep Cherokee Main. Req'd light on all the time...other problems

[Jerry Casper <gremlingts@xxxxxxxxx>]

  My ailing aunt has a '91 CHerokee with a "few" miles
on it. It has a red text message lit on the dash
saying Main. Req'd on full-time. She said the
mechanics said it'd be $400 to shut it off, or leave
it on and ignore it. Anyone know what it means or
refers to?
  Another problem I found was it was 3 quarts low on
oil. When wiping the oil filter block housing, it had
a thin seeping line of oil at a seam where it's in two
pieces? Is there a bolt which joins these two pieces?
The oil filter is angled UP, not to the side or down.
The seam is below it, a straight line around the
circumference. When I wiped off all the old crud, I
could see fresh oil seep out continuously while the
engine was running. Is there an easy fix, like
tightening a bolt, to cure this? 
  Since I'm learning about Jeeps, figured I'd throw
this one out as well, to help my aunt. Thanks in
advance,

Jerry in Virginia
back to work tomorrow, dang it!

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