Where to begin???
Seals, check interstage seals; shaft packing, spill strips, etc., and replace or retooth as necessary. Bring all back to original OEM clearances.
Blade erosion, rotating, and stationary blading. Specialists will have to bring nozzle and stationary stage blading back to original contours using welding and blending techniques.
Cracking. Shafts, rotating blading, tip tennons, etc., all rotating parts will have to be checked for cracking by a variety of means, depending on how detailed you want to get. Shell bolting should be checked for cracking. It can be as simple as visual, or as technical as magnaflux or dye penetrant.
Nozzle block erosion/first stage blading erosion. This is usually a high wear area needing remedial attention.
Last stage(s) blading (bucket) erosion. Some have erosion shields. Check condition, and correct as needed.
Valving. Stop and control valves must be checked for stem and shaft cracking, as well as bushing and packing clearances.
Bearings need to be checked for excessive wear, and corrected if found to be out of tolerance.
Oil lines need to be checked, cleaned, and possibly flushed.
This should be enough to get a little conversation started. If more comes to mind, I will return and repost.
rmw