ONAN Transformer Radiator Oil Leak

Many years ago I came across an outdoor mineral oil filled transformer that had been patched and sealed with some sort of epoxy. It did not leak. I really can’t remember whether a fin or a header, I’m tending towards a fin, a small one, like 3” across.

I think that there is a fix for you that will be less cost than draining the transformer and welding up the leak.

The repair is a 2 step process, where a temporary fix involving a proprietary Belzona compound is used, making the area suitable for a permanent repair.

However, based on your photo, access to the leak could be very difficult. Perhaps a consultation with a Belzona application engineer could give you a plan.