I agree that there is nothing wrong with modern fillers when used properly, and I have tried to discourage the use of lead many times. I think the use of solder for circuit boards and wiring is more akin to tinning the metal than applying the lead, in that the metal has to be hot enough to melt the lead when tinning. It has to flow and be spread with a rag to be sure it has the whole surface covered.
But when applying the lead that is not the case, and that is where I messed up. The metal only has to be warm enough to accept the lead. If the metal is not warm enough the lead will crumble or not stick properly, so it is a very delicate balance. If the metal is too hot and the lead melts, then it will be harder to work with the paddle because it changes the structure of the lead. It can also cause pinholes in my opinion and lose of adhesion.
Leaded areas from the factory may also have pinholes, and it is not a major problem as long as the metal at the bottom of the hole is tinned. And I have checked that with a sharp pick and a magnifing glass. Here is a picture of a factory leaded seam and yes it will have to be cleaned up before painting.
And a close up
When filing the lead out at the edges it is easier to tell if you have good adhesion or not, when it gets really thin it will curl up.
So as you see in these shots of the hood, that there is no adhesion problem, it feathered out nice, although there are a few small pin holes, just like the factory lead that has been on there for 55 years.
So I will repeat this again. Lead is very difficult to get right, and I do not recommend that anyone use it.