If you fell it is time to change it change it.
The only warning please take the new thermostate and place in pot of water and bring to a boil with thermometer and verify that it open at the right temp. The QCA on these are not great. There has been a bunch of us who has gotting bad one's.
PEH back flushes his fuel filter, I don't know about oil filter. And if very frugel and that works for him, I just wish he could let other maintain and spend their money as they like since they earned it.
He has a problem with "pre maintance."
And when you over heat and ruin a head I don't think he will warrent you cost to replace it. So please consider the source and conquences.
Charlie