The rear door doesn't open with the same "spunk" it used to. I think it is related to the gasket/shocks. Any suggestions on how to get them working better?

I'm guessing you mean the rear hatch, if so, the only fix is to replace the rear gate struts/shocks. they do get old, and do lose their lift/support. they are very simple to replace, just find somewhere to get the new ones ie: nissan dealer, courtesyparts.com, etc.... and you will be able to see how they remove by looking at the new ones in hand.