PS leaks

[Mike <mac50@columbia.edu>]

Excuse the novice question, but I was looking at the archive and saw an 
old thread about oil-based fluid being accidentally used instead of 
mineral-based, resulting in very leaky hydraulic systems and/or ruined 
gaskets.  Then I thought back, to my horror, of the (apparently) leakey 
fluid resevoir on my newly-purchased 89 100 I saw the other day.  How can 
I figure out if the system has the correct mineral-based fluid in it?  
I'd hate to have to replace the rack because of someone else's mistakes.

Replies appreciated!

Mike