I tend to agree with jryffel on this at least here in the states. Some compressors you could maybe do without too much trouble in the field. Some I would avoid altogether. Add specialized tools, manuals, equipment, labor and the cheap cost of factory remanufactured units makes a better job. In some parts of the world though it is common practice to rebuild screws and from talking with some of the fellas doing it they have quite good results. I'm not sure if they are doing it on a bench or what. Probably it may be cheaper to do that considering the location and cost of shipping a whole compressor and shipping the core back or availability. Andy sounds familiar with rebuilds on screws and I would also tend to agree that 12K is short for a bearing change. More like 50K + with vibration analysis. Some of the smaller hermetics units I work with are pushing 40K without any internal work, just yearly oil analysis and no vibration analysis.
Larger open drives, definetly do vibration and oil analysis on a regular basis.
Mike Hopkins