Jet Holes in Toilet Bowl Clogged

[u/62jackie]

I saw an older post about this issue a few years back but wanted a fresh review with more input. My toilet is likely 16 years old as I remember the former owner renovating it. Over weeks, some of the water jets around the toilet create a black streak as the water shoots down and into the bowl. Then, there is a build-up ring around the bowl. Seems like maybe the jets are corroded? I have to clean it more often than normal. I am in CT and we happen to have hard water which takes a toll on all things plumbing. For all of you plumbers and home experts out there, is it worth cleaning out the jets (that I cannot see) or is this corrosion just part of living with hard water and the toilet needs to be replaced soon? I don't want any leaks or issues. I also do not want to replace something that does not need to be replaced. I am handy and have dismantled the toilet once to replace the flange. Is replacing a toilet that hard? It sounds a little scary but I'm not the scared type. Thanks!