how do I repair a steering gear box gasket on a 1987 chevy G20 van
It's usually cheaper in time and money to just replace the whole steering gear box instead of bothering with taking it apart and replacing the gasket. You can pick up a good steering box for pretty cheap from a wrecking lot or get a rebuilt or new one from an auto parts store for a good discount if your core is rebuildable. Typical guidelines for being rebuildable are (from LMC Truck): "A rebuildable core will have no excessive wear. No worn, broken, scored, or damaged, cracked, frozen, or rusted housings. No broken or damaged mounting points."
Thank you for your help