The day my "onboro ALFA" would revive

Regarding the clutch master cylinder which I repaired the hole at piston with solder , one of my friend advised me that the solder might not be hard enough.  Therefore , I tried the repair again in another way. Disassembled the clutch master cylinder again. Now I can do it very quickly because I disassembled brake master and clutch master cylinders many times J Heated and removed the solder at the piston hole. I used the soldering iron instead of the burner because I heard giving too much heat on piston should be avoided. In this time , according to the advice from my friend , the repair method is to screw in the thread with strong adhesive into the hole , then grind the thread head to make the piston surface flat.  In order to do it I bought bolts and a grinding stone at the hardware store. Cutting the bolt to adjust the length to fit the hole depth.  Engrave the minus groove at the cut bolt head to make screwing in possible with minus scr