All ICF rakes(EMU, DEMU,MEMU & Mail/Exp) has a tenure of 25 years to run on the tracks of IR after which it needs to be replaced mandatorily as because it covers the total effective route kms for which it is made. Periodical Overhaul can't make the coach either brand new or make the wear and tear of the concerned rake Zero which it got after running a certain route kilometers on the tracks of IR. It can just prepare the coach to run some extra time if there is paucity of brand new coach. After 25 years tenure it won't be prudent to run these old haggards on the railway track from the viewpoint of passenger's security.
If Periodical Maintenance solve this...
more... problem then all Coach factories will stop their production of new coaches and shut down their workshops.