Rebuild?
Its not clear to me what the "spring mounted pulley" is, but it sounds to me like your talking about a stand up block that is acting as fair lead. If its only the sheeve that has degraded, AND... depending on the block load, you may be able to replace the sheeve for cheap and reuse the carcus. I have rebuilt merriman blocks with degraded sheeves in the past. The right size generic delrin sheeve with metal bushing that will fit merriman blocks can generally be found at West Marine or other suppliers for under 3 bucks. The axels on many merriman blocks look something like a clivis pins that has been peened over one of the cheeks. Drill out the peened over axel with a drill press (like drilling out a rivet), pop in the new sheeve, and replace the axel with the same size/length clevis pin locking in place with a cotter (under 2 bucks). I've had no problems with refurbished blocks in light load, non-critical applications. Note: It is unlikely that the retaining cotter will ever be as strong as the original peen over especially if the cheeks can experiance a lot of lateral torque. I wouldn't do this on a critical high load block....Be Careful.. Use Judgement Garhauser prices are very reasonable if you decide to replace