I have my sling three years now. I've noticed every year & only when it gets really hot, about 100 deg. for a few days or so there was a drop (nothing more) of fluid on the garage floor. After time I noticed my clutch fluid just a bit low. My thoughts are that on those really hot stretches' the fluid expands enough that it expands beyond what the bladder can handle and pushes out the top cap. Again after three years this only happens on extremely hot stretches.
Well, it certainly gets hot here during the summer, but I've never found any evidence of leaks on the garage floor. I just didn't like how dark it was, so I'll be checking it regularly.