I needed to replace our PacBrake because it had failed again (the butterfly valve shaft had become frozen and it would not actuate). I had previously removed the unit and worked the butterfly valve shaft free and lubed it up well, then reinstalled it, but it failed again within a couple hundred miles of driving. I am presuming the shaft has become too galled to be successfully rehabilitated.
I have now purchased and installed the latest technology exhaust brake from PacBrake, a Pressure Regulated Exhaust Brake (the PRXB model). This one promises to provide much more braking power at lower engine rpm, giving us a much wider and more effective engine braking speed range when going down steep mountain grades. The new PacBrake with new clamps came to about $1200, and it took me less than 3 hours time to install (including testing).
The secret is to provide PacBrake with the serial number from the original PacBrake, and they will determine the exact PRXB model that is a drop in replacement. They do not sell direct, but their website lists several distributors. I ordered through OregonFuelinjection.com.