Fire sprinkler maintenance

[Amy A.]

I am considering the purchase of a large old apartment building that has a sprinkler system.  I will be calling the fire dept. to ask about past inspections, etc.  However, in my pro-forma I have no idea what expense to include for sprinkler system maintenance and repair.  It is a wet system on the first 2 floors and basement and a dry system on the 3rd floor.  I believe the system was installed in the 1980's. 

 Do any of you have experience with this? What should I watch out for?