I recently noticed my ELC compressor was running excessively, and that led me to notice the top of BOTH of my rear shock bodies had rusted through. I priced a set of replacements with Chris, but then stumbled across the 580-338 and 580-339 for $374 and $327 respectively on Amazon. I bought the last 580-339, but there are two 338s left. I'm sure it could be adapted to use on the "wrong" side. Get it while you can!
ACDelco 580-338 Rear Shock Absorber with Upper Mount by ACDelco http://www.amazon.com/dp/B001KSA2IG/..._hVOftb0MY4XG0
Naturally, my compressor was toast as well. It still ran, but didn't actually push any air. I removed it and began to take it apart, and it looked like it had been pumping salt water for a few years. No kidding, it was that pitted and oxidized inside. As I needed my car back immediately for a trip to Groton, I ripped the pump out of a LeSabre at the pick-n-pull, shoved it in the STS cradle, epoxied the lines in the air output since the connector wasn't compatible, swapped the plug from the old STS pump to the donor, and hooked it all up. It does the job, but it sounds terrible. No more double rubber mount isolation, it's metal-to-metal. I'll resolve that soon enough, but that's an option if you're in a bind!