just to add to it. I too have welded my 8.8 tubes and have yet to have any problems with them. but just to throw another wrench in the gears here is some more info on cast stuff.
"Please allow me to explain in simple terms why welding any cast material is bad in terms of strength. When you weld material that is strain hardened, such as virtually any and all formed steel material, the material from the 2 different pieces flow together and meld, with the rod being used as a catalyst, or a helping hand. Now, castings are different. In all castings, be it cast iron or cast steel, there are tiny pockets of air between the individual particles of metal. These air pockets are also present in forged steel during it's formed stage, but they are relieved during the strain hardening process. These air pockets play a big part in the makeup of castings. When you attempt to weld cast material, the air pockets restrict the flow of molecules, thereby not allowing the two materials to flow together and meld. So the flow is basically one way, from the non-cast part to the cast part. Now, forged material hardens as it cools, and this process is not very critical in most applications, due to the structure of the materials, however with cast, the hardness is reduced as it cools, allowing the casting to become brittle. This fact is true with all cast materials, be it aluminum, steel, or iron. Cast material cannot be heat treated once it is cooled after it leaves it's casting form. Welding to cast material is not a matter of whether or not you've weakened the casting, but rather how much have you weakened the casting, because once cast is welded, it is weaker than it was originally. This is why nobody welds new new arms to the flat top knuckles unless they are uninformed idiots, my friend. Another problem once you've welded to cast, is how much you've weakened the casting. There is really no exact way of knowing, so the part may last a week, a year, or a lifetime, but the fact still remains that it is now weaker than it was.