Comparing a Repaired Versus New for an Electric Motor

We have done several years of research on recycling rotating electric machines. We have tried to identify new guidance on this matter. We conclude:
1. There are cases where a rewound motor is better than a new one. We have the opportunity to design the winding tuned to the application. The result in this case might be an upgraded motor.
2. The biggest problem we identify in our research has been mentioned by several discussions. The magnetic core might suffer degradation during repair works. Efficiency is reduced. A new motor might have higher efficiency (improved magnetic materials compared to the old motor).
3. We recommend to repair the motor in most cases. Generally, you don't have the trained engineer to do an economic study. Furthermore, in most cases you don't have another option. If you buy a new motor, you play safe. Availability of the new motor is another item.
4. Don’t use aged magnetic materials.

It's good to know that there are repair shops like yours. Unfortunately it's rather exception than standard. The question whether repair or replace is often heard and there is no one good answer. You have to take into consideration size of the motor (its cost actually), scope of repair to be done (again cost), how old the motor is (if it's old the design and rated parameters may be much worse than those of modern motor; I especially mean efficiency as it determines LCC), availability of good repair shop. I will publish soon report made by Institute of Electrical Drives and Machines KOMEL (Katowice, Poland) some 10 years ago which covers this subject quite well. Despite fact it's fairly old its valid and all conclusions apply.

I'm working in a power plant in engineering department.
we have motors with this specs: 37kw-3000rpm(2pole)-frame: 200L-400v delta- 50Hz- ins class:F- installation type with flange(IM V1) this motors applied for oil pumps.
we have relatively high damage rate in these motors.
my experience in repairing in this electric motors: if damages only in winding and rewinding them usually we have no problem but when we have mechanical damage such as wear off in bearing housing or shaft bending reconstructing was not so effective and we deal with future fail in motor performance and its expected life time.
I'm believe you in this fact that we can repairing damaged motor in a good condition and it may be better than substitution by a new one but we not have a exact criteria for this question when repair and when a new motor?