these are supposed to be like that fella to take up differant ride and road settings ie move around as the wheel goes up or down or when turning
i think if this makes sense
also is the clip on the inner c.v joint still presant as this is what holds it in the box itsef
my series1 popped out after a few miles and lost its g/b oil
took it out pulled th clip out a bit and put it all back in and its been fine every since
also you could have nicked the drive shaft seal when you fitted the shaft in