You need to decide if you want an LSD or a TBD (torque biasing diff, like a Quaife). If you want a real LSD, I would go with Guard, and if you want a TBD, I would still pick the Guard over the Quaife, as it's a better unit, and actually, cheaper.
Guard indicates theirs might not fit certain 99 5 speed gearboxes. I literally have to break mine open and let them know whats inside! Wont consider Quaife. Havent heard of gbox? Any links to that one?
There's a new company called Wavetrac that will be releasing torque sensing LSD units for the 996/986 6-speed in January. Their system is unique in that it has the ability to provide locking when one wheel is completely unloaded, which normal torque sensing LSDs can't do. It also claims to provide longer life and more gradual locking than competitors. On top of all that, it's cheaper than Guard by quite a bit. You might want to inquire with them, maybe if they get enough interest, they'll develop one for the 5-speed.
Guard indicates theirs might not fit certain 99 5 speed gearboxes. I literally have to break mine open and let them know whats inside! Wont consider Quaife. Havent heard of gbox? Any links to that one?
I'm curious as to why you won't consider Quaife unless you are going for a true LSD? I have a Quaife installed on my 2002 S and it has been the best modification I have made (I autocross a lot). I bought the unit from Autotech who was very responsive and shipped mine within 24 hours of the purchase.