Sounds like you might have a leak or there is something else failing. AIOs should not have this issue and unless your PC is near a very steamy shower or around anything else that could have deposited this moisture, chances are that you have a problem.
I agree with Gam3r01 here...sounds like the AIO is failing in some manner. Your best choices involve replacement:
1) Return to the place of purchase, provided you still have the receipt and you qualify for the return policy.
2) RMA the cooler to the manufacturer assuming it is within the warranty period and you still have the original purchase receipt. Make sure you read the warranty requirements carefully; some require you have registered the product within 30 days of original purchase to qualify, or possibly some other requirements. That being said, some companies might be easier to get replacements from, others might not.
3) Get a different cooler and use it instead. This is likely going to be the outcome of either 1) or 2) anyway, to some degree.