a few years ago I let the bowl completely dry out once when i had a long spell in storage.
after that I couldn't get the ball to seal. I researched and tried all sorts of things...cleaning it, lubricating it, etc... nothing really worked well. At some point I even tried some seal conditioner from tehtford.
I'd read that it's often caused by hard water deposits and I tried cleaners like CLR...but still not a long term solution. Some of these made it better, or even fixed it short term, but not fixed
As a last ditch effort while I waited for the new seal to come from amazon, I poured a strong CLR solution in the bowl, fairly deep so it would take a while to leak out. I forgot the specifics now, but basically I soaked it for a few days keeping it submerged, every now an then I'd step on the pedal a bit to let some solution get to the sealing surfaces better. So after maybe 2-3 days (not sure how long it was) I found that it wasn't leaking by....
since then, I diligently keep the bowl flooded. As part of my putting into storage routine I have taken to pouring a bit of the blue tank treatment chemical in the bowl and maybe 1/3 or so full of water, just so it's extra deep and will take longer to dry out. I tried it once thinking that it might slow the evaporation rate slightly....(I really have no idea if it does or not, but I still do it.) I keep a close eye on the water and add water after a few weeks as needed when it's evaporated a bit.... it's certainly not leaking...well at least not more than a drop every week or so
this was a few years ago now!...and I still have that new seal kit I ordered floating around in the garage someplace.
ps. I went and checked my order history. I bought the seal January of 2017.