I build universals dry with blue loctite on the joint set screw. I then hang them from the table with masking tape and then fill each cup with maxima chain lube for motorcycles. When dry, I work the universal and clean up excess with a rag soaked with motorspray. Good stuff.
Diffs, I use AE Diff Lube (red label) and on thrust bearings, I pack them with Mobil1 grease (red stuff)
I can't say that my Tamiya diffs are super smooth but they work. Anybody else have ideas?