Metabo Grinder W7-115 Quick -2 issues

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The (00715421) grinder is well used and now only operates intermittently. This was preceded by some operation where speed would drop off occasionally. Have read guides and think it's the switch, but wanted to get another opinion. It could be brushes, but I don't think it's the cord. What do you think?
Also, I can't positively identify the part that locks the wheel for disc changes, which is worn out (you press #49 to lock wheel) . I think it might be the bolt (#52). If I do find it, I have no idea if it's possible for me to replace it. If you can help on that one as well, I'd appreciate it.