On our 93, I changed both of the units behind the bumper because the coils were starting to look pretty rough. They might have cleaned up and a new compressor would have been enough to get them going, but new coils make for better cooling so we did that. Parts are about double in price (changing entire package versus the compressor) but the labor will be a little less. We still have one original unit (bedroom unit) that works great, but its much louder than the new units.

Next time I have one changed, i will insist that they charge the unit with nitrogen and watch it for a couple of hours before charging it with freon. Both of mine had connector leaks that required return visits.