1994 Toyota Camry How long will a Fuel Injector last?

Hello. Six days ago on Monday, I started smelling gas fumes through the vents. The place I took it to said it was the intake manifold gasket, so I had that replaced the next day on Tues. Wednesday morning I let the car run with vents on to try to blow out the smell in the vents, only it got worse. Looking under the car, there was a puddle of gas. Took it back and was told it was a pinched O-ring on an injector. They fixed it for free. Today on Saturday though, gas smell returned and more puddles of gas. Same people tell me now I have a leaking fuel injector, and if I pay for the part, they'll install it free.

What is the typical life of a fuel injector and could this just be a case of them damaging it, and trying to cover themselves?

I bought the car 8-9 years ago with 72,000 miles on it. It now has just over 120,000, so I haven't been hard on the engine at all. Any help would be greatly appreciated.