The thing I’ve never liked about minivans is that it’s difficult to get to the engine to do any work. This means it takes more time for a mechanic to maintain or repair the engine, and it’s going to cost more than it would if it were a car, truck, or SUV.
It might be worth it to rebuild or replace the engine if this were another type of vehicle, but the fact that we’re talking about a minivan makes this easy. It’s time to let this one go and buy your next vehicle.
Unless there is a particular reason a minivan most suits your needs (rather than a car, an SUV, or a crossover vehicle), I recommend getting something used that is cheaper to maintain and repair.