I'm still sitting on 5 unused seal stones (2 x 2015, 1 x 2016, 2 x unlimited) and a big stack of FGs.
If not for Christmas or New Year's there's still the FKG anniversary at the end of January - that's when we had the last 30 FGs promo gacha, which I hope will appear again.
So in the next 3 months, we will have quite a few occasions to get some seal stones.