Just because your engine hit TBO doesn't mean it needs an overhaul. Many engines run for hundreds of hours past TBO. It all kind of depends on the history of the engine and some voodoo that no one can figure out.
I'm no mechanic but I've been around aircraft my whole life. I've seen engines flown right need work at half TBO and straight up abused engines run a long time over TBO and everything in between.
But yes it's always good to have cash inthe bank when playing with aircraft.
