I simply used a gas tank liner to fix tanks with very small pin holes like that before and they've all held up great. no need to heat it up n destroy the paint

akara - sealing sounds like a terrific option since i would hate to toast my clear coated faded paint
can you recommend a particular brand of sealer?
thanks
 

I tried red coat on a DT100 tank and it did work for a while but the tank had so many pin holes and some larger seam issues it eventually failed. I don't think it was a fair test and this product seems to have lots of fans out there. If you go that route make sure you let it dry for at least a week and that you can't smell any off gassing still occurring. The tank has to be completely clean, free of moisture, rust, oils and you have to be fast with it before it dries in clumps. Worst case if doesn't work and you have to remove it. I think acetone will get it out. Lots of youtubes out there on this one.

I HATE liners.  Most make such a mess when they fail...  and the thicker ones always seem to fail.  Could have have been poor prep?  I don't know, it's always been on used bikes someone else lined.

That said, I did use POR15 fuel tank sealng kit on my MG1T...  has held up for years.

 

My goal is no leak and not destroying visible finish, so perhaps I buff the seam down and solder edge (one of the few things I can do well) or have same mig welded?

so much great input, going to sleep on this and see what happens with my offer on an alternate tank and then act. 

I would recommend TIG over MIG. 

But if you know how to solder and can get the metal clean enough to stick, that should work awesome. 

From my experience, having silver soldered both seams at the rear of the tank on a DT1, it just doesn’t hold up to the vibration long term. Looks great, doesn’t leak for quite a while, but eventually opens back up. Brazing is so much stronger but definitely will destroy your paint. 

I have patched several with J&B Tank Weld, Petrol/fuel resistant. Can be pressed into hole or split and surface cleaned, let cure and touch-up paint.

I've used the POR-15 and it seems fine, but given the choice in this situation I would have it TIG or MIG welded.
I don't want to have to deal with a failing liner in the future.