Those cheap hinges aren't just a build quality thing, they're a warranty dodge play. By the time the sag shows up, the builder's one year fit and finish window is long gone and the homeowner eats it. The real fix is codes requiring anti-sag hardware on gates over a certain width, same way they did with balcony rails after enough people got hurt.

Was it really that bad or just some dust in the corners?

How many miles did you have on that coolant when it tested weak at 18 months? Trying to figure out if it's time based or if heat cycles are what kill it.