Depends on the buffer type to be honest. The OLEO ones are still somewhat current on the network so can be overhauled, but at a somewhat exorbitant cost. Unfortunately we are finding that some types can not be overhauled now. Wheel sets if a suitable size can be machined down to a good profile, but obviosuly there comes a point where the wheelset becomes scrap. They can however can be overhauled, but the cost of it is eye watering. One of our brake vans sustained damage to its wheel sets, and the overhauller had to change the wheelset to be monobloc (all one piece of metal including the tyre) to a tyred wheelset! The tyres I think ended up coming from South Africa!