I don't have a lot of knowledge about the XL-515.
After John Saul died Bob Rodgers continued running MicMix and he, along with co-owner Bill Allen, did the '515.
The work I did on downward expansion to shorten reverb time that was used in the XL-515.
That same circuit, after being tweaked by Bob Rodgers, later became the DynaFex.
The transformer was likely made by a company called Texas Transformer.
I suspect that it has a 20-0-20 and approx 8V windings and could be replaced with just about anything capable of producing +/-15V and 5V outputs.
You might disconnect the transformer secondary to make sure that it's not a blown diode or filter cap causing it to overheat.
Judging from the coloring of the lacquer it has gotten quite hot.
You also might look at replacing the whole assembly with a Meanwell switcher.
http://www.jameco.com/webapp/wcs/stores ... _237367_-1
There are a few Meanwell's having both 5V and bipolar outputs.
I have about three in stock and have been wanting to try it with the Dual Class-A.
I think Roger Foote uses the Meanwell in some of the FCS series.
They are far quieter than the specs would indicate.
The above is 5V at 4A, +15V at 1.5A and -15V at 0.5A.