Some info in this thread: http://www.homebrewtalk.com/f35/perlick-o-rings-222382/
I think that should cover #5 and #8 below. The other stuff you may not need to replace.
The plastic/rubber parts include two different sizes of o-rings, two different sizes of rubber washers, and a pair of bearing cups. I'm not sure of the sizes and Foxx Equipment catalog doesn't list the sizes. If it helps, here are Foxx's part numbers and a diagram.
3 12G09-131 Washer (rubber)
4 12G09-185 Bearing Cup
5 12G09-186 O-ring
7 12B03-173 Washer, faucet
8 15C07-104 O-ring, plunger