i cannot remember how this joint is made but assume they are just black rivets that it pivots on?
-if so -there is not much you can do apart from introduce a small amount of paint or -dare i say it -glue to stiffen them up.
have repaired the electrical connections on Tizio in the past but not come across this - although i have the same problem with a another classic lamp called the Dove by Nemo italianaluce which i am considering exactly what i have just suggested to you as it is completely sealed.
good luck
dom, December 2010