would it leak if:

Ok your talking about 2 completly different things here,

Your T5 Transmission takes ATF!!!

NOT GEAR OIL

Repeat,

DO NOT PUT GEAR OIL IN YOUR T5 MANUAL OR AUTOMATIC TRANS

I use Mobil 1 Synthetic ATF for my Trans, Works like a charm, and yes 3 quarts is what u need,

For the REAR END

Thats where you use Gear oil,
And no nothing has friction modifier in it. You have to buy it seperate from Ford,

3 quarts and your Friction modifier is what you use for the rear end,
And again id suggest Synthetic Fluid
 
well that is what i meant, i know not to use gear oil in the tranny. so i guess i do have a bad rear seal. no biggy and i thought it had it added, that sucks, how much is it and do i need one bottle