the two plates are made of plastic and are general blind plates which are used for this bases, if no valve is destined for that specific location on the base. The plates are tight, otherwise our entire principle of valve islands would no work.The liquid is normal leakage spray, but could be anything that makes bubbles. Out of the 288 items now tested, we only found 12 incorrect. We will scrap them on our site along with the 42 other ones and debit them to you with our new NCM.