I think they have maxed out their life expectancy. I suggest you research some new varieties or replace with the same variety in the spring. I also suggest you uproot the old grasses in very early spring and then improve the old soil with some organic matter and add some Osmocote slow release plant food before adding the new grasses. The mature grass clumps will have depleted lots of nutrients from the soil over the past decade or so. Keep growing, Marianne Binetti