Several times I think this kind of thing is open for interpretation. One mechanics concern is another's trivial item. Other than Tom, are there any other IAs that would like to chime in please?
To clarify the story, the "mechanic" was the one I use who tends to get a little moody and pops off with things he doesn't mean and blames it on the heat, his schedule, his aching body..etc. I work with him and another aspiring A&P mechanic every Saturday. We recently just finished a Cessna 182 that had been sitting in Scottsdale for the last 12 years so there was a LOT of things wrong with it. Anyway, the pilot next door to me (Brian) mentioned his primer and I said, "Hey, I bought two kits from Spruce. You can have the other one." So today my mechanic asks me, "When you worked on Brian's primer, do you think that was legal?" I said, "I didn't work on Brian's primer, he did and yes its legal with a log entry as owner." He said, "Pretty sure that's not part of the 31 things you can do as owner. (there's only 30 mentioned in Part 43 appendix A) You can't mess with the fuel system. So you think you can just go in any of these hangars and work on airplanes?"
That's the part that thoroughly cheesed me off.
All I said was, "You know better than that. You know ME better than that." And I turned around and walked away and don't intend to speak to him anytime soon. I went home and got my copy of the Part 43 and started reading and I'm still convinced an owner can do this but my opinion doesn't matter to the guy who signs off my log book when the real A&P stuff needs a signature.