Interesting thread this one...
In my case the 1959 Ken Ryall track bike I referred to here a few days ago arrived from the ebay vendor with an undeclared (but obviously 'old') "tank-slap" ding in the top tube.
The frame is otherwise straight and the paint finish pretty good but with plenty of 'patina', but I spent a few days pondering whether it would be worth sending it to Mercians for a replacement tube and re-enamel.
Couldn't make up my mind and in the meantime I bizarrely found the name of its original owner / rider - a gent who raced with the Redmon CC in London, written on a yellowing piece of paper rolled up in the handlebars under the bar end plug.
I contacted the club to see if they remembered this chap - they were very helpful and an interesting story came to light about him that sadly discretion will not allow me to share with the list. This tale did not have any direct bearing on the damage to the head tube (which Redmon CC could not explain) - but was sufficent to persuade me not to touch the bike and leave in its original trim.
I'm now of course rather proud of my 'ding'...
Ian Briggs
LUTON - UK