My keen ear (at least for certain frequencies) has noted that my rear suspension compressor has been cycling more frequently lately. I installed a ~$830.00 a few years ago and don't want to burn through this one, so tonight I went looking. Soapy water in hand, I found my right rear shock is leaking. Of course not where I'd expect (air line connector, bladder, etc). The leak is around the underside of the upper mounting plate. Perhaps this was a weak point for these. ACDelco has changed up the part number from 580-348 to 580-1039 so they may be a slightly different shock. The new number is specified for FE3, F55, A8Y (code on the shock), just like the original.