I keep hearing this, and its silly.

For one thing, foreign supplied hardware is frequently repaired in foreign countries.

For another thing, a sad truth is this: In peacetime in America, armored vehicles are maintained with a goal towards making them last forever. They do crazy repairs like do a complete rebuild every 6000 miles, with other lesser repairs like rebuilding the engine every 1500 to 2000 hours, with one of the seals needing replaced every 360 hours, replacing the treads every few hundred miles, etc.
In combat in Ukraine, these tanks will unfortunately regularly hit a mine or get hit by a Koronet WAY before they hit 360 hours of combat. And then they will suddenly become parts sources.