i have a 69 camaro that i started to strip down to the bare metal, the quarters have been replaced with skins that wrap over the top of quarter about 1 inch, after removing all the bondo on the seams i noticed it was brazed every 1 1/2, it was done approx 8 to 10 yrs ago, it didnt have any cracks in it shoud i just mud it back up or mig in between the brazing? is there a special filler i should us over the brazing?

I know we brazed things together for years before Tig/Mig came along. I haven't done it in a while now but it makes a good weld. Only thing I've ever heard bad about it in connection with auto body is adhesion problems with some fillers and paints but I think some of that was due to the flux that was sometimes used.

If it held up for 10 years w/o problems, let it be. I would use a etching primer on the metal then epoxy then fill primer.

Use a fiber filled body filler first and then a polyester. The fiber filled has better structural characteristics that allow it to adjust to different metal expansion rates without showing up as a "shadow line" or cracking.

Also, hopefully some sort of sealer or glue was used if the panels were overlapped by 1 inch, otherwise there may be a path for moisture to enter from the back side and begin rusting under the filler.