I successfully removed many a tube ding/dent with a set of special tools ( I think Bicycle Research made 'em ) which were comprised of a square block with the appropriate tube diameter drilled through and then halved. We greased the curved surfaces of the block, put the halves together around the tube, but the assembled blocks and frame into the bench vise and twisted and more-or-less pulled the tube through the blocks. Supreme judgement and experience was required to know what size ding could be fixed. Sometimes the paint was destroyed in the affected areas, sometimes you'd never know. Boy, a picture would be worth a thousand words here. In these modern days of umpteen different tube makers and sizes, I doubt these gadgets are around much anymore. Life was certainly easier in the days of one size suits all Reynolds 531. But a machinist-pal could probably make you as set of these blocks after measuring your tube diameter? I mean if the alternative is to refit the tube, what's the harm in trying? On the otherhand, how much bondo has been employed over the years? Only the framepainters hereabouts could answer that I reckon.
Ricardo Bulissimo Verdi Nevada