I don't see it as an issue. When you register, your home state will see the addition and levy a tax if applicable. California will never know that an out of state resident bought an airplane and took it out of state. Yes, the prior owner will notify the county of residence that he is no longer subject to annual property tax, but the county guys don't talk to the state guys. Even if they did, they typically don't have an issue with a non-dealer sale. To be certain, call the California Tax gurus.
See this link: https://www.cdtfa.ca.gov/industry/ve...e.htm#Aircraft
"You may not be required to pay California use tax if the only use of the aircraft in California is to remove it from the state and it will be used solely thereafter outside this state.
This exclusion only applies to a purchase that would otherwise be subject to use tax. No use of the aircraft, other than to remove it from the state, can be made. This exclusion does not apply to a purchase from an aircraft dealer subject to sales tax.
Delays for emergency repairs made to the aircraft must be verified as functionally necessary for the aircraft to continue its departure from the state. You must provide supporting documentation such as fuel, repair, hangar, and/or lodging receipts to verify the property's departure from California, plus documentation showing that the aircraft did not return during the applicable test period."