Why is micropad dirty only on top side not side where green is??

by Jose
(Lawrence,Ma.01841)

I just recently noticed my motor chamber had a slight leak on my xp4,and with that said I opened it up and cleaned up inside then silicones it on groves,now it has no more air coming in but looks like it's working,can see debris flowing down in canister but my micropad is only getting dirty on top closet to motor and seems dry on green side!!
A: I really don't know you might want to contact the manufacturer, Mars Fishcare, directly about this. Also, posting this question may get some other readers to comment.