Buy a Quaife LSD. It's good quality and garunteed FOR LIFE! Plus no replacing clutch packs etc.. Remember, if your 240SX didn't come with an LSD you will need a drive shaft from one that did or order a new one. The driveshaft off the 240s that have LSD are shorter.
Note: Buying of a Quaife LSD is my opinion. There are many others out there to choose from. I believe all the 240SX LSDs are interchangable aka S14 & S13