I have an older version of one of these: https://www.zojirushi.com/app/product/cvdcc
For taking care of them, the standard procedure is to run them in "cleaning mode" with a full tank of water with a packet of Citric Acid dissolved. That works really well for removing the mineral deposits from inside the tank.
Recently, I noticed that there was rust-looking stuff coming out from the upper lid, so I replaced the upper lid. However, the deposit is still there on the edge where the lid touches the tank.
The standard procedure of descaling them doesn't work here because you are not supposed to fill the water that high in the tank. How can I descale this? I imagined that the lightweight version of a full descaling process would be something like wiping the edge with a paper towel soaked in lemon juice, but that didn't do anything.
This is what it looks like: