I too have a Mk3 2002 Dci and had an issue with the tailgate. While Roys comments are good and these things do need oiling, I am also amazed at the truly dimwitted design used on mnay parts of my Espace. I own a twenty year old BMW and its doors always open, rusted up or not. I think its a typically French foible. They are very Avant Garde in many of their designs, but often use poor design and crappy parts or poor solutions to many very obvious and simple things that you wouldn't find on a German or Japanese car. If you make somehting well, designed simply then it simply won;t go wrong in the first place. Door handles, locks and catches should just work.
I would love to know how to open stuck tailgate too - am sure it will affect me one day!
Apologies to you all. It seems the Series 3 Espace does not have the normal release override that other Renault models have. Now I have had a look at one, it appears they have really badly designed this one, since if the tailgate is stuck closed, it is even extremely difficult to remove the interior trim, which is the other way to access the catch and release it.
It makes it even more necessary to lubricate the catch regularly, and keep the contacts clean.