Its more like having to completely replace the lining. Would the PVC tube have to be pulled out the case entirely, then relined and replaced into the case?
1. Take the nails out of the bottom using a tack puller. Be gentle and don't bend the nails.
2. Remove the bottom gently, don't force it.
3. Push the tubes out through the bottom.
4. Study the way the tubes are put together. Use a razor to cut out the tube you need to replace the liner on. If the liner is just torn a little on the top then you can simply sew it.
5. Remove the tape which holds the liner in and remove the liner from the tube. Insert the repaired liner or the new one and fold it over the ends. Tape it closed using packing tape.
6. Re-insert the EVA foam at the bottom of the tube and tape the end of the tube closed.
7. Put the tubes back together.
8. Tape the bottom so that the the tape cannot roll up when you insert it.
9. Insert the tubes and stop short about 2" from the bottom.
10. Spray some glue into the bottom 2" if you want it to be a little more secure.
11. Put the wood piece back on and replace the nails.
12. Set the case on the floor and push the tubes down all the way until it seats at the bottom.
Done.
All this takes 30min to an hour depending on your ability and it's not as hard as it sounds.