I drove 1800 miles in a Hydrogen Car

The lady who said that you could leave the car in the garage for your entire life and the tank would still be full is either naive, lying or is being creative with the definition of "full". It is impossible to constrain hydrogen as it's molecules are smaller than any other elements so regardless of what material you make the tanks from there is going to be leakage. It is physically impossible to restrain something much smaller than what the intermolecular distance is in the restraining object. It's a bit like trying to restrain golf balls with a basketball hoop or water with a woolen jumper. The hydrogen tanks have a rated permeation rate in the range of litres of H2 gas per hour. This works out to something like 0.1g of gas per hour. The gas tank holds about 5kg so you are theoretically losing a tankful of gas in about 6 years. This permeation rate does change as the pressure in the tank changes but personally I feel that my lifetime is going to be much longer than 6 years it takes to empty the tank let alone the much shorter amount of time where you could still call the tank full.
Dianna your father is right. The salesperson is wrong. It's not a high rate of leakage but it's still significant and a lot of the regulations for hydrogen cars are to do with the leaked gas.