Thanks, everyone. Bry, your trick usually works, but this time, it's pretty bad. It's GRADUALLY, bit by bit, day by day, loosening up again.
I think you guys are probably right about water getting behind the gasket. I can't think of anything else it could be. Visually, there is nothing out of the ordinary going on, and water and air are invisible, so it must be one of the two!
BTW, Bob, the user's manual doesn't even mention backflushing in their cleaning/maintenance instructions, so I think it's best to follow their recommendations. Some machines aren't meant to be backflushed, like Chris touches on in his post. Although, it did come with a blind filter, so there are some mixed signals there.
Chris, in response, this machine stays on constantly, and it is used pretty heavily every day in a large office setting, so the temp of the metals stays constant. It works reliably every day til get crazy and decide to clean it.
Thanks for the input, guys! Good stuff!
It came with a blind?