If you can find out the type of paint you bought, any local Benjamin
Moore paint store should be able to explain the "lifetime guarantee".
You may be dealing with a "prorated guarantee" like the kind you get on
tires. That is, if the paint doesn't last even one year, you get almost
all of your money back. But if it lasts 30 years, you get very little
back. But, it's worth checking out.
Guarantees and warantees, in my view, aren't any benefit to the consumer
because they effectively limit the manufacturer's liability to the cost
of the materials purchased. So, if you were to use Brand X pistons when
having the engine in your car rebuilt, if those pistons were to fail,
then Brand X would only be obligated to provide you with new ones, or
refund your purchase price, at their option. But, it's still you that
has to pay to have that engine rebuilt a second time, and are you gonna
wanna use that set of new pistons you got from Brand X under warranty
this time too? Prolly not. You're going to want to go with someone
else's pistons this time so you don't get a bad case of deja vu because
you stuck with Brand X.