Repair or not?

We have a 1997 subaru outback and the engine block needs to be replaced. It has about 135000 miles and the cost of repair is about $3500. Should we repair this if we need the car for about a year while our son finishes high school?

That’s impossible to say without knowing a lot about the rest of the car. E.g. How likely is it that the transmission will be next? How old are the tires? Brakes? Suspension?

I always just ask myself one simple question: assuming that [X repair] has just been done would I be willing to spend [$X] to buy this car? Or put similarly, if I take [$X] out to the used car market would I be able to get something better?

The car is 12 years old. Replace it.