The other day I was riding my 87/88 Schwinn Circuit, that has been fully chromed, and the downtube came loose from the bottom bracket lug. The lug also has a crack around the cutout. I took it to a local framebuilder and he told me he could fix it by filing the lug and replacing the whole downtube. I understand that this is a costly and involved procedure.
Why can't the the lug be filed and the downtube just be re-brazed? Will there not be enough penetration? Would the joint not be strong enough? I'm just having trouble understanding why the bike has to be disassembled to re-braze the lug.