Hi,
The standard SRX silencer is built like a tank.....so should take a weld ok, as long as it's not gone paper thin, in which case you may have to weld a patch on.....strange to get a hole in the top.....I would imagine the battery breather pipe is hanging over the top of the silencer (instead of routing down in the right hand corner of the swingarm) and acid has rotted a hole in it.....?
There are some good aftermarket silencers about, don't know whether they still make them, but I have a slightly modified predator on #4, whose pic you can see in the current gallery, about half way down
cheers