If it was stored inside, I wouldn't worry about it. I'd change the oil and expect it to be ok. If it was outside for a few decades and there could be a lot of humidity, it probably would be worth checking out.
Interestingly, I'm in a similar situation. For some reason, I don't have 5th gear any more and I don't consider myself competent to work on a transmission. I will be giving it to a local manual transmission shop with a copy of the workshop manual. I don't think it requires any skill that shop that works on manual transmissions doesn't have.
The problem you might have is if you need parts. Alpine-America in Canada deals with Renault parts and they might be helpful (
http://www.alpine-america.qc.ca/). I would probably try r.d. enterprises (
http://www.rdent.com), Dave Bean (
http://www.davebean.com), or JAE (
http://www.jaeparts.com/) first if/when you find out what you need in case they have it.
Good luck! Post some pictures and tell us what your plans are.