i rode my onset two days already without any problems, while everybody in the cable park expected it to break in the first five minutes. stress cracks could be from wood getting wet.. maybe... anyways, here's what i did to my onset just before i rode it...
sealed the fin holes with epoxy and coated the whole deck with marine urethane (4 layers)
sealed the top deck screw hole with epoxy (filled the hole halfway with silicon first) to make sure it's water tight
unless it's an Oak or New, wooden wakeskates IMO needs to be sealed up real well before riding it the first time.