Help/advise suzuki rm 125

Hi guys I've recently bought an rm 125 2003 model. The bike is a really good bike. All fully rebuilt etc. The only issue is. The first time I rode it the gear shifter went very floppy after a couple of gear changes. I've stripped it down and the locating pin that sticks through the selector fork has snapped of from the casing. I'm not sure what this part is called I'm sorry. I'm just after some advise.....

Can this part of the bike be welded or is it going to have to be a new crankcase. I'm really annoyed as the bike is absolutely immaculate apart from this problem.

Any help/ advise would be greatly appreciated