Apartment problems

My wife and I have lived in our small apartment for 7 years. In that time, we have had virtually no contact with our landlord or real estate agent.

The only problem is that, although we've done our best to look after the place and keep it clean etc, after seven years things begin to fall apart. A bad smell often comes up the drain into the shower room, and the sliding screen doors, for example, hardly slide anymore.

My question is: Who is responsible for paying for the upkeep of an apartment? Obviously, we carry out minor repairs as and when necessary, but when it comes to something more major, is that our liability too?