Glad to hear you found it!
What plate do you mean? The circular hold down plate with 4 bolts? Or the large separator plate? (see answer below)
Now that you have the VB off, you should install new VB gaskets.
If you also want to replace the snap ring that broke, (good idea to replace it... it is weakened... thats why it broke....it's the one that holds the OD band servo in the case) be aware that it can be a b**ch to get the broken snap ring out.
Also when re-installing the OD servo it is very difficult to get the servo pin to engage the band.
If you have not already removed the rest of the broken snap ring and the servo... here's a tip.
Make or borrow or buy a tool like this >>>> http://www.etoolcart.com/aodeservopistoncompressor.aspx and install the tool FIRST before removing the snap ring. Turn the pressure screw on the tool so it holds the servo in place. That way the servo stays in place and you don't have to fight to get it back in and possibly miss the band... and then have to pull it all apart again. The spring under that servo is fairly stiff and can be alot of trouble to re-install.
Here's another tip... look very closely at the large steel separator plate that goes against the case. Look in the area of the rear most accumulator, the one that has the goofy looking little "hat" type spring retainer. (2-3 accumulator)
That retainer has a kind-of pointed knob that puts a little dent in the separator plate. If you look very closely you will probably see some very tiny cracks in the plate at that point. NO GOOD! get a new plate.
One like this >>> http://www.cascadetransmissionparts.com/4r70wheavydutyseparatorplate00up.aspx