I've just thrown away a Burnerd 5" 4-jaw for the same reason. The body itself was the worn bit, as the jaws are a lovely fit in my newer 4-jaw. I kept the jaws as spares. So assuming yours has suffered the same wear, I don't think there's a lot you can do to recover it, short of machining up a chunk of cast iron to make a new body! (In that respect, I think the major difficulty would be forming the screw threads into it.) It may be possible to machine away the existing grooves and let in some chunks of material, but the effort involved would be immense.

Unless you like doing that sort of thing, I suspect your only solution is to buy a new chuck. I got one from Ketan at Arc Euro (the Zither Indian ones) and it's very good for the price.

Before buying, I'd had a look at a lot of the Chinese ones sold by Warco, Arc and others, and the problem with them is the stupid chamfers they put on the front inside corners of the jaws. You can't grip anything thin with them.

Don't scrap the chuck body … think of it as a tee-slotted faceplate.

MichaelG.