I registered just to say that we have had a Maxx 8 for over 5 years (Model Number WTE86300AU or WTE86301AU, I dunno which) and it started having this problem where the Container light would come on after 5 minutes no matter what we cleaned (condenser container, filter, lint trap, inside of the filter compartment, inside of the slot the lint trap fits into), it just kept coming back on and the dryer would stop.
Clearing out the "secret flap" has fixed our problem! It looks like water was pooling in there over the course of time, hence the sludge and the need for an absorbent cloth (I started with paper towels before realising there was so much water in there).
One of the other symptoms we did note was a pumping sort of sound when you switched the machine on again, like it was trying to move some water around and not succeeding.
Hooray for the internet and for Google search!