How To Repair The Damage Of Oil Transformer Fin?

It has a long procedure

See here

Sealing Transformer Oil and SF6 Leaks Quickly and Effectively

What are the circumstances regarding its acquisition of the damage? How old is it? How much use does it see?

See http://cr4.globalspec.com/thread/68736

Talk to the transfomer manufacture.

If it's not leaking, my advice is to do nothing. Transformer may operate slightly hotter, but that should not be a problem

I agree with Mr. Pugh. If there are no leaks, you are probably okay to continue running the transformer unless you have it loaded so heavily that you need every last bit of cooling. Only some of the inner tubes appear crushed enough to restrict their oil flow very much. The other rows of tubes in that radiator don't look like they were affected, nor the other radiator behind it. You will want to clean up the scrapes, and prime & paint it well, so that it doesn't rust and eventually leak.

You will also want to monitor the radiator regularly. Watch for leaks not only in the dented areas, but also at the flange where it bolts to the transformer tank and the welds at the bottom tube and the manifold. There appears to be some distortion at those spots, and cracks may form but take a while for oil to leak through.

How did you get that kind of damage??? It looks like a truck backed into it, but it is on the inside, between the transformer tank and the tubes. I would have expected to see it on the outside of the radiator.