Welding onto alloy is a bad idea. My dad had a hole in his R6 casing about a finger width and needed it repaired. Tried welding it and it just melted before the other metals could "stick". I would say , you would be better with a new casing part , that way , there's no chance of it leaking or smashing or whatever. It might seem cheaper but honestly , its not! Since its a stressed part , that's even more important.Welding alloy introduces weakness.
If its a scooter , you should be able to get the bit you need for buttons (tiny engine , tiny price)
Also , I didn't do the welds myself , the bloke that did it has been working with alloys for years , my dad knows him personally. Ended up buying a whole new engine as it was cheaper than buying a casing.