ok there is a large o ring that goes all the way around the top i rest right in the lit where the male part on the base unit sits its a flat right there also is a o ring in the under that white part for the bubble build up tube check pull all your baskets out again and re aline them i set mine in wrong when i just reassembled it just now they should sit just a little lower than the lift tube and the lid should sit almost in place then bolts only hold it down from the pressure,, there also would be to o ring on your barbs for the hosing that might be the source as well, are the grove on the lid filling with water? or is leaking down the side?
one more test pull all your media out and run it empty does it still leak?