The few air/hydraulic rigs I've worked with have been a maintenance nightmare, and they weren't as old as the one you're looking at. I'd suggest that you do a thorough brake system inspection, and rebuild/replace anything even remotely suspicious, particularly flex lines front and rear.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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