What rules allow a student pilot to add oil to an airplane? A private pilot oral exam guide I'm reading asks a basic question about an issue I had taken for granted:

You have just completed the first leg of a long cross-country and notice that the oil level is approaching the one quart low mark. As a private pilot, can you add the quart of oil yourself or is a mechanic required? (See 14 CFR Part 43)

Clearly this must be preventative maintenance? No. 14 CFR Part 43 Appendix A does not explicitly list adding oil as preventative maintenance.
Searching online I found a lot of forum posts discussing this issue, some suggesting it is &quot;obviously&quot; preventative maintenance per the definition, but 14 CFR Part 1 does not define preventative maintenance, and others suggesting it isn't maintenance, it's servicing, but this isn't defined either.
How does this work if you're a student pilot on a solo cross country? If you shut the engine off and check the oil, are you stuck if the oil is low?
The best answer I can find is adding oil is not &quot;maintenance&quot; or &quot;servicing,&quot; it is Normal Procedure per the Pilot Operating Handbook / Information Manual. The Cessna 172S POH as part of the preflight check on page 4-10 states:

Engine Oil Dipstick/Filler Cap -- CHECK oil level, the check dipstick/filler cap SECURE. Do not operate with less than five quarts. Fill to eight quarts for extended flight.

The POH is a little ambiguous how much oil to add, but it clearly states the pilot executing this procedure should add oil.
I believe this how a student pilot can add oil to a plane, or at least a Cessna 172S. Is this correct or is there a better explanation?
The FAA doesn't consider adding oil to be maintenance. The Hochberg (2016) interpretation says:

The subject of adding oil is often debated; however, we note that it
is not an item included in part 43, appendix A, paragraph (c), which
lists items the FAA considers to be preventive maintenance.

Also see the FAA's Flight Standards Information Management System, under Elements of Maintenance (emphasis mine):

In broad terms, it has been generally upheld that basic servicing
tasks, such as fueling and adding oil, are neither maintenance nor
preventive maintenance. But even that has some caveats. When adding
oil requires a precise sequence of steps or partial disassembly to
gain access, then that would be considered a maintenance activity.
Adding oil to an oleo strut for example, would be a maintenance
activity, whereas adding a quart of oil to a GA aircraft would not.

Since adding oil isn't maintenance - at least not in a simple GA aircraft - part 43 is irrelevant and there's no requirement to have any type of certificate to be allowed to add it.