Hairline cracks on sides of rail of a used CA P90 The Red Dot Module housing was damaged too... Clean off some paint to see the crack better. It was recommended to also carve the crack some to get a better fill. Clean, add flux, heat the part to ~350, and add solder. Sandblasted the part after the first round, had to re-solder after it failed. Careful milling, the solder smooth and sand blasting the part for paint.... ...and after 8 attempts and the part hairline cracking along the solder every time I said screw it and milled the top flat.