

Haven’t looked into it but do shops offer lube analysis services? Yeah you could send out your own sample to a lab, having it as a shop service would be way more accessible to people.
Though, in my experience, getting people to commit can be a pain, lots of “yeah I know we have a long p-f interval and it’s super noticeable before it functionally fails, but it’s not that much effort so I’m doing needless maintenance anyhow just in case”, which end of the day you do you.
Terminal usage is a tool just like GUI tools, I don’t think it’s helpful either to preload people with the belief that it’s some arcane tool that takes years before you can start using it, like anything you pick it up by doing.
Can’t really say it’s 100% optional as a blanket case either, heavily depends on a user, my work I’ve depended on having a terminal for years, and that was even before I moved into SWE, I’ve seen lots of business developed processes put together as an amalgam of batch files, VBA/VBS, and python because they needed to put something together with what they had rights to.
Be honest that I don’t see the terminal as a barrier to Linux anyhow, for the use case of “I browse the internet and use office programs”, you absolutely do not need to drop to the CLI, at least not for Debian or Mint, can handle installs and updates through their graphical package managers. Most people probably aren’t setting up services or the like on their machines, and if they are they already require terminal usage on any operating system.