Sample schematic here: http://www.reelschematic.com/schematics/Shimano/Shimano/SHIMANO%20MLZ-60(1981).pdf
Full MLZ range here: http://reelschematic.com/schematics/shimano.php
Two drag disks - one above and one below the spool.
The lower may be Teflon, which I wouldn't grease.
I find some older spinners are a bit jerky under load, no matter what you do (ie upgrade to carbon fiber and grease etc).
It may be the case here.
There may also have been a tiny bit of wear somewhere on the braid, compromising its integrity. A touch more drag may have been a touch too much...
Not sure if that's of any assistance, though!