Oil leak at 100K? is this common? what to do?

What is your question?

i have an oil leak, but it is leaking somewhere inside the engine: ie: it's not on the ground. my mechanic thinks this will be too expensive to fix, and that i should probably just turn it in and get another. a friend told me she'd heard that this is a common problem with Prius at 100K. i have 164K. what is the best course of action? it seems it will cost $$ just to find out what is wrong. thanks tracy