kitch428 is our Toyota specialist and he can tell you exactly what's involved. Often, you need to compare the time and material costs associated with repairing the old compressor versus installing a new compressor/clutch assembly. Most compressors are ready to be replaced around 100,000 miles.
Several months ago, the rotor pulley bearing on my 2000 Ford Taurus needed replacing (103,000 miles). The effort involved was about the same as installing a new compressor. Therefore, I went ahead and installed a new compressor/clutch assembly and accumulator ($300). Now, I should be ready for another 100,000 miles or so. For perspective, here's what was involved:
http://www.askmehelpdesk.com/cars-tr...ml#post1722090
If you decide to install a new compressor/clutch assembly, or evaluate your current system, this writeup may help:
http://www.askmehelpdesk.com/cars-tr...ml#post1864159