buggirly

Dear Friends, Please can someone advise me about my problem? I have a 2001 Outback Limited that is not quite 4 years old (and not quite yet paid off!). I have 73000 miles and my warantee is done. During the last two weeks, my car started squealing upon acceleration, shaking upon startup, and making generally worrysome noises from the engine...and finally the check engine light came on and the car started smelling like gasoline. I just moved to the area and took the car to my local subaru dealership. They said that my 3.5 year old car needs a new fuel injector, rear differential, and quite possibly transmission work. I have asked them to replace only the fuel injector and I will take it for a second opinion. BUT what I am wondering is : Has anyone had to replace their r. differential? Also I don't tow anything and I don't do a lot of off-roading. Is it common for the transmission to have issues so soon? I am a graduate student who took a loan from my parents to buy this car. I guess I would like some advice about how to deal with this. I am by myself and am not very mechanically oriented and don't want to be taken for a ride. Thank you very much for any help.