A common occurrence with all TKS® porous panels is "leaking" when not in use. Specifically, panels will stream very small quantities of TKS ice protection fluid while in flight or drip when parked. This characteristic is normal due to the porous panel design.
CAV Ice Protection is here to give more information on your TKS® Ice Protection System and porous panel "leaking". Brian Sader, Repair Station Manager, gives some insight into the topic.