Trans Am Mysterious coolant leak

99 TA, sitting in storage in my garage. Not driven alot in the last few years (maybe 2k in the last 3 yrs). Not a contiously heated garage in Ohio, but temp has only gotten below 32 a couple of times. Then one day started to leak coolant. Not much, maybe a pint. I put sawdust on the leak, so the garage cat wouldnt drink it. Moved the car the other day and reparked it in a different spot. No leaking going on over the past week. Car still is full of coolant so its not empty. Did a quick check from above, and didnt see a anything. Havent gotten under to look either yet. What is the typical cause for this mysterious leak? I would think that if its gonna leak, then it would be consistent, not just be random. thanks, Nathan