I decided to clean an old Optimus 111 that I have had for a while, and I know it works well. A simple job that turned into a nightmare. On trying to remove the tank from the case one of the bolts unscrewed from the tank easily, but the other just spun around. At first I thought the thread was stripped, but it turned out that the bolt was stuck in the female threaded insert, and both were spinning round but still in position in the side of the tank. No amount of penetrating oil and patience would solve this one so I had to cut the bolt off to remove the tank. I have never examined one of these female inserts before, but it is a double insert and the inner threaded one was loose in the outer case. If I brought a strong magnet close in, the inner would move about 1mm out of the outer case, but I couldn't remove it or get the bolt stub out. No problem! I will solder the lips of the inner and outer cases together, drill a hollow near the edge of the bolt stub and then tap anticlockwise with a punch to remove the bolt stub. Then, while tapping, disaster struck and the whole insert assembly fell into the tank. Thankfully the steel bolt stub was still in the insert, so it was easily removed through the filler hole using a telescopic magnet. I decided to replace the insert with a blank nut fitted from the inside of the tank. First I had to solder a steel plate on one side of the nut and trim it so it would fit through the tank filler hole. Then I had to roughen the inside of the repair hole using a Dremmel grinding wheel and then degrease the inside with a pipe cleaner and meths. Before I removed the Dremmel bit with the telescopic magnet, I tied a piece of string on it so that I had string going inside the tank from the repair hole and out through the filler hole to help locate the repair nut on the inside. I didn't want to risk using solder again in case I melted the blank plate joint, so after threading a stud onto the repair nut and tying the string to the stud, I cleaned and pre-loaded the nut surface with JB weld, and then pulled it into position through the repair hole. Then I suspended the whole tank from the string and filled around the outside of the hole with more JB weld. After a 24 hour cure in the airing cupboard the JB weld was cut back and the stud removed. The tank leak tested well under pressure, but I feel I can make the repair stronger. Instead of using solder and JB weld, I could braze the blank plate onto the nut and then solder it into position. Has anyone else had any experience with this sort of repair? I looked through the threads, but I may have missed some relevant ones.