I recently took a look at the stamped brass negative battery terminal
(1.9l have both pos and neg stamped) on my '89 and found it suffering
from fairly severe "season cracking" which is a form of stress
cracking that brass is subject to.  It wasn't visible with the
terminal in place but it considerably affects the integrity of the
terminal and I will have to replace it.  Might be worth pulling them
off to take a look inside and make sure they're not all cracked.

Yours,
David