Sanding sleeves are installed at the head of the jack, and as the elevator runs, it mildly sands the piston down. This is used to remove nicks, dings and scratches from a piston that has multiple points of issue. It wI'll reach 99% of the relevant parts of the piston. By simply using the overtravel and hand sanding the remaining 1% all of your piston that could go through the packing will be sanded.

That being said I find it odd that you had a leak, were re packed, and then blew the seal completely. Just reading here, it sounds like the repack may have been faulty as I would have expected it to simply leak again. The damage on the piston must be pretty substantial, as all re packs I have ever done, I checked the piston for marks to sand down as I did not want my brand new repack to meet the same fate as the old seal.

No your usage should not be held accountable for any damage to the piston. If the elevator was left in the down position for those first 4 years, and someone cleared the head of debri, it should have worked straight away. If the elevator was left up, there is the possibility of rust developing on the piston due to moisture in the air. 4 years of it would be substantial enough to damage your seals.

Hope this helps, and if you are in doubt, get a few bids from competing companies for the repair. You may be surprised by someone else's assessment. Good Luck.