I prefer that we use more specific tags whenever possible to reduce misuse (assuming we aren't running into length issues).
So even if we end up with other types of "maintenance", tool-maintenance is the proper tag for the maintenance of tools.
That being said, depending on usage, this may end up being too broad, in the same way that tools is considered too broad. Someone who knows how to maintain a knife may not care (or know) about maintaining paint brushes or pen nibs.
This may be something we start with a broader tag and then, when it becomes clear whether these questions make up a large enough volume of questions here, it may be better to break them up by tool and create tags like knife-maintenance and pen-nib-maintenance.
Note that it's not generally good practice to use tags to "append" onto other tags. There's no "official" way to do this because the meaning of the tags don't "combine". So, using knives and maintenance does not really imply knife-maintenance. Much like on SO, tags for specific versions of programs or languages are made rather than making tags for a program and a tag for a version number and expecting them to combine like the Planeteers combine their powers to create Captain Planet.
That being said, some sites use this method to help with some tagging issues - for example, on Movies.SE, some titles are too long, particularly with series, so they use harry-potter in conjunction with prisoner-of-azkaban. This is non-standard and usually forced due to tag length restrictions.