To address your opening concern, buy it but don't add it but carry it when the read out is down to 2000 miles range remaining.
That way what is in the tank will soon be fresh.
Using that plan you only need buy a small amount, enough that whatever happens you get to the service, and what you buy will not be overly wasted.
That way what is in the tank will soon be fresh.
Using that plan you only need buy a small amount, enough that whatever happens you get to the service, and what you buy will not be overly wasted.