The process of repairing transformers can be a dirty job. But tearing down a transformer can be very educational and technically rewarding.
I recently had the opportunity of disassembling a defective transformer for a local utility. This transformer is part of a 1950's vintage transmitter used to locate "system faults" on a 4,800 volt distribution system.
Closely evaluating designs during their disassembly provides a technical education of design aspects that have been successful, in some cases, for many years.
Carefully monitoring the disassembly can often provide knowledge of why the design failed, thus providing an opportunity to improve the device when re-manufacturing.
Researching the techniques used by the original transformer manufacturer.
Satisfy a customer. Supporting a customer in maintaining equipment of older technology is often a valuable asset.
Repairing a transformer provides an opportunity to recycle reusable material rather than adding to landfill.
In conclusion, disassembling and reverse engineering a failed transformer can be a dirty job and the process is very educational.