My '95 325i (manual) has it, and I would have guessed that most 325 's have it.

Also, was it standard on some models, or an option on all models?

You don't have one. Advantage is on tight corner your inside wheel won't spin nearly as much, allowing you to stomp the pedal more. Dis- advantage is your inside wheel won't spin free, so it's easier to loose control. You'll also have more tire wear. %25 lockup is good, more than that should be for track cars only unless you have deep pockets for tires.

Can anyone inform me if my 94 325i manual trans. has a limited slip differential? If not what are the advantages of having a limited slip differential (25% 50%) etc. Better cornerning/handling? Better or worse take off acceleration? thanks for all the ppl who post.