If I'm on your shoes, I should tell the new owner of the letter.
If I'm the new owner, I will be glad that the parts will be replaced for free and have a better 2nd hand car. But maybe my problem will be, if I can afford the labor from the casa which is a lot higher. It may not be on my budget at the moment.
But when I bought a 5 year old car, the first thing I did is to have it checked at the casa to make sure that my drive will be at least worry free.