This depends on how deeply you want to dig into it. Those teeth do NOT look happy! However, from your description of the issue I'd guess a bad starter drive (what us old-timers call a "Bendix") is the immediate issue. Unless you want to dig in there I'd pull the starter and take it to your local rebuilder (most towns have someone who does this) for an inspection and repair as necessary. If it were mine I'd have them rebuild the whole deal - it just makes sense once it's apart and on the bench. So that'll be the drive, bearings, brushes, and whatever else it might need.

BTW - IIRC these are the only bolts on the engine that use 12mm heads. Not an issue for me 'cause I've worked on lots of Japanese cars and have a good stock of 12mm wrenches, universal sockets, etc. Been a while since I had my starter out but that's my recollection.

Dan