Adrian, I hope that everything works out with that car bro. Unless you really plan on beating the crap out of your car, or going totally performance, I wouldn't go for the LSD.
Normal driving will not kill your tranny, nor will moderate driving... You just have to watch your take-offs. Like Joe said, you should never launch the car with a factory setup above 2k RPM. The LSD is very expensive, and the install costs almost as much as the part itself. So we are looking at spending close to a grand to get it all done. (unless you do it yourself...)
Now, if you plan on making your car into a total beast, the LSD is the only way to go. Othewise, I suggest you fix the car now, and be more careful when you drive it.
Best of luck man.
!!!!! 