*** Toilet Trouble *****

You may just have had a piece of ....errrr... 'undigested corn or peanut' caught in the seal groove, that finally got dislodged and dropped into the black tank.

Jim, "Manure occureth."

If your toilet is like mine... adding water after a flush is done by lifting up on the peddle. I'm guessing it's not the additional weight of the water nor the fact that additional water was added but it's due to lifting up on the peddle... which forces the ball valve closed. Chances are your return spring may need to be replaced or the track for the ball valve needs a good cleaning.

We use plumber's silicone grease to lubricate the toilet seals after cleaning. Never had a problem. Home Depot carries it in the plumbing section. Comes in a small jar.

I pour a little mineral oil in mine when it is sitting. It keeps the seals working smooth just like it does to you if you take a little. Also keep the dump valves working smooth.

I also use it to wipe down all my cast iron cookware after use. I would not be without it.

The weight of more water.

That extra water is probably keeping the Blade Seal wet. Are you sure there isn't debris (usually toilet paper) trapped in the area the Blade seals against? Parts availability depends widely on make and model of toilet. Price can be prohibitive.
We have the much maligned Thetford AquaMagic IV but the doggone thing has always worked, and will hold water above the blade if I add some after flushing. Cheapo thing, but then it's a toilet, after all...