Don't panic Shaz.........at least it failed while it was still with Toyota and you have a loan car.
I would expect that they will only charge you for the initial new rocket cover gasket, and not for the second gasket + labour due to faulty installation.......would that be right Ethan?????
Rocket cover gasket failures can be messy........they may give your engine bay a clean at the same time! Make sure you have them show you the engine bay before you leave, and make sure the engine bay is clean.
The next time you go in, make sure that you request for the most senior mechanic to work on your car, and remind them of this incident......you are the customer, and you are always right!! .....and tell them how important your baby is to you - they always appreciate someone who loves their car!
I am sure everything will be fine, these things happen sometimes :-)
Cheers, M