Sorry, I'm new to this site hopefully you still will be reading responses. I've done a few Martins, bari's and teonrs, they have soldered on tone holes. Before going on I will caution you that it is a good idea to "wire-down" the tone hole in the event of over heating, this will melt the existing solder and dislodge the tone hole from its current resting place and then you have to do the whole thing. Not fun if you have little or no experience. Careful with the wire so you don't scratch the surface of the horn. The key, is as mentioned prep work, make sure the pieces to be soldered are cleaned. Either with emory cloth or, depending on the application, a sharpened pick of some sort. I have made one especially for tone hole soldering. Scrape the joint, using care and be precise as to not skate across the body and create more problems. Also when fluxing the joint to be soldered use just enough to cover the joint. Solder will follow flux. It sounds like this is the situation at your other tone holes, bad prep work, too little heat, impatience. You have to make sure you've heated the area hot enough, which can only come with practice. Dip the tip onto the metal, not the flame, and see if it readily melts and flows. If it does you're laughing. Hold the heat there till you see it flow to where you want it, where you cleaned and applied flux. I'd practice on something else so you get a feel for the solder and heat. I remodelled for some time and did extensive plumbing. You might want to get some 1/2 copper pipe and a couple of elbows and try soldering them together. All the same principles apply except for the scraping. These joints need less precision. Good luck