how serious is a leaky left valve on my 06 prius? miles on drive belt before rep

did not seem serious which is why I did not get it done. I had to slam on the brakes hard when a car cut in front of me to avoid an accident back in 2008. I want to make a trip up to LA to see my sister; I live in san diego. I have 72,000 miles on the prius. I really don't drive very much; to work and back mostly. 20 miles. The drive belt has wear but seemed like it still has many miles left before really needing to be replaced. I had a basic Toyota truck for 20 yrs and everytime I had to brake hard/unexpectedly, the brake ____ would pop and needed to be replaced. the prius seems to have the same design flaws except the parts are of better quality with intricate engineering hence expensive repairs? Everything seems to be working fine. A sympathetic Toyota car rep told me a while back to keep an eye on it (friendly advice)... LEFT FRONT TIRE AREA. THERE IS LEAKAGE/WET RESIDUE ON CARDBOARD ON GARAGE FLOOR NEAR THE FRONT TIRE AREA. I THINK; COULDN'T BE ANYTHING ELSE? I AM IN DENIAL; BUSY. I WILL CALL DEARLER & FIND OUT WHAT IS LEAKING. TRANSMISSION FLUID? OIL? BEST TO HEED THE SIGNS/AVOID MAJOR PROBLEMS. THANK YOU FOR YOUR HELP, LET ME KNOW WHAT YOU THINK. NEED TO JOIN PRIUS CLUB CHAT & GET INPUT LIKE YOURS.