Are you sure they are going bad?if you replace it and it runs alright for a short period of time and then starts sputtering again, you've got a problem elsewhere.
Which part of the distributor is getting damaged? If it's the terminals then here's two things you should check first:
1. Are the screw holes in the distributor body damaged? The body is plastic and the screw holes are very, very commonly cracked, stripped, or broken on the Vortec distributors. If they're not both in good shape the cap won't stay on straight and can get damaged. If the screw holes are damaged, you can try to get by with zip ties around the cap, or replace the distributor.
2. Hold the rotor and try to move it sideways in all directions. You should have barely any noticeable movement. If it moves a significant amount, then the upper bushing in the distributor is gone and it's letting the shaft walk all over the place. Time to replace the distributor.
I'd also suggest replacing the plugs, wires, coil and module at the same time to make sure you've got a solid base to start diagnosing from if the distributors really are going bad.
Let me know how you get on.Pete.