Gear diff / suspension issue in Blitz ESE

[Spoolio]

I've posted my problem in the HPI section but just in case the Trucks section gets a better view I thought I'd repeat it here.

Just finished the rear end on my ESE. It's all as per the manual except with the addition of gear diff instead of the ball diff. Once past the "driveshafts level" point there is no more up travel available on the suspension without the turnbuckle and driveshaft starting to bend .

If I take the shocks off the rear end stays up on its own . The driveshaft seems to be the problem as it's too long and so there is no more room for it to go into the diff any more to allow the suspension to compress. If I take the silicone o-ring out of the outdrive then my problems go away as this seems to the clearance that I need.

So I guess my question is, how crucial is the o-ring?