According to the factory manual, it must meet GM specification 9985010. I grabbed a bottle of STP Power Steering fluid I have, and the label says: Meets service requirements for GM, Ford, Chrysler, AMC and most foreign cars. Look for similar wording on the bottle you buy.
You can add power steering fluid to your 1988 Chevy Astro by removing the top to the power steering fluid reservoir. Pour the fluid directly into the reservoir.
under the hood
It does not matter on that year as long as it is power steering fluid.
The Astro Van power steering and brakes work off the same pupm. Check the pump for fluid. If it's full and the brakes and steering still hard you must replace the pump
check the power steering fluid, also check to see if the belt is on
it should be a black cylender cup thing that says power steering fluid
In order of MY observations: connections, hoses, power steering pump and finally rack or steering gear, although rack is becomming much more common.
there's a reservoir tank under the hood the cap says power steering fluid which should be near the brake fluid reservoir
power steering fluid
a light greeny blue
The fluid reservoir should be built onto the power steering pump. There will be a cap on top to fill through.
I have a2005 malibu and it has electronic steering no fluid needed