Well said Nino, Ditto Owen   

10 years seems a long time for insert changes though????

I'm assuming heavily played machine would be sooner, and perhaps the purists would change sleeves almost annually to keep their pride'n'joy in peak condition???

Thoughts?
MM.

Really depends on the coil assembly... Flipper sleeves should be changed at least every flipper rebuild. But for Pop Bumpers and others, you may decide not to change them at all.

The sleeves do get dirty, and will hamper the plungers ability to freely move inside the coil, but for many assemblies it is not really noticeable.

It doesn't cost much to buy the sleeves, so if you decide you would like to do it, then by all means do so.