Main Board relay locking up?

Machine fails to power on with press of power button. For a while, unplugging the washer and plugging it back in would allow the button to work and power the machine on. There was a faint 'click', which I assumed was the relay on the board resetting and thus allowing it to power on again.

But after a while, even this was not working. Sometimes unplugging it for a while would allow it to power on, sometimes it took hours, and repeated attempts. I was about to drop a couple hundred bucks on a new main board, but before I did, I started trying all kinds of random things as a sanity check.

One of these things was that I opened the door, reached in and turned the drum about a quarter turn by hand, then pressed the button... and it powered up immediately. This has been working every time, first try, and without fail for the past month. Also of note, it gets through whole cycles, and never fails when powered on. It's only when it's done and powers down.

So I'm guessing there's some kind of drum interlock sensor as part of the logic chain that allows it to power on? Anyone care to enlighten me on this one?

NOTE: It's not the door lock sensor... I did try merely opening and closing the lid a few times and that does NOT allow it to power on. But as soon as you rotate the drum a bit... presto... it works just fine.