hi
2 bottles of oil went in dont sound good that
when you have the car on level ground and remove the allen key bolt you should just get a show of oil coming out so if 2 bottles went in and it aint coming out of the driveshaft seals sounds like the gearbox has been running with seriously low oil so might of knackered the gearbox but i am just going on what you have said
i had a problem with screeching when pulling away upto 20 mph then it went but that was a wheel bearing on the front left
mark