Mildewey smell from GE top loader

My GE top loader has a bad mildew smell for the last 2 months. I’ve tried vinegar, which was useless and bleach which helps temporarily. The tub definitely drains. I popped the front and disconnected the hose and checked the hose, pump and drain hose for blockages but found none. I can hear some water sloshing around from an apparently sealed section at the top of the tub. Should water be in there and could it be the source of the smell? I was thinking of drilling holes in the bottom of that section but thought it wise to consult with you experts first.
Thanks in advance for your help!
TPTDC