Calcium (?) buildup in toto Drake sipon jet

[Sandman2]

Our Toto Drake is about 9 years old and was not flushing well. Used a small mirror to look at the sipon jet and it was discolored and seemed to have a buildup that was restricting the opening. The large 3 inch opening was fine.
Has anybody heard of this? And if it is a buildup - any ideas on how to open it back up?
Thanks.

 

[Sandman2]

Finally, bit the bullet - grabbed a 6" round file (fairly rough) and started filing away at the buildup. Lots of material slowly broke or rubbed away. Probably doubled the size of the opening. So it was definitely some kind of calcium/hard water/? buildup. Toilet flushes much better now. Kind of tempted to drain out the bottom and soak the whole thing in "CLR". Anyway, still curious if anybody has noticed a buildup like this in their sipon jet?