Phil Allison wrote:
"Sparky"

This cap was removed from a 70's-80's German industrial machine:

http://i37.tinypic.com/10psxg3.jpg

It has no polarity markings.

** Bull****.

One terminal is common with the metal case. Is
this always an indication of the (-) terminal?

** Yep.

The base has molded terminal locations numbered 1-4, two of which are
empty:

http://i36.tinypic.com/e6x542.jpg


** Are you totally blind ????

The usual cause applies ?????

FYI:

The markings are clearly 1, 2 and 3 with the fourth a NEGATIVE sign
!!!!!!!!!!!!!

Are they? Their order is a bit strange if so.

On the other hand, take the - to be a 1, and the other symbol to be a 4
with a bit missing, and you have 1, 2, 3 and 4 in a normal order. So the
situation is far from clear enough to form a basis for installing a
replacement.

Sylvia.