have a colnago master x light with a 3mm deviation in the top tube and a kink in the tubing underneath the top tube near the lug.Rather than scrap the frame my local garage is happy to weld a piece of steel to the underside.It will look dreadful but will hopefully salvage the frame for training purposes.Are they any precautions the welder should take and should the weld be done in a particular fashion given the nature of columbus gilco tubing.
If they are skilled in welding very thin wall tubing they may be able to do it.
Honestly, I would not do a thing. This frame is, IMHO, junk at this point. I would only use it as a get to the grocery store bike.
There are many nice Taiwanese frames that are superior to your Colnago (Sadly, alll Colnalgos are made in Taiwan anyways) or there are budget oriented custom framebuilders in the US that can make you something great!