Roof maintenance?

[Narnia]

Hi everyone, how often does the roof need to be sealed with caulking? Also, how often does the roof need to be replaced? Is conditioning necessary? We are considering a 2010 3000RK and from the pics, the roof looks pretty dirty.

Also, can you pressure-wash the walls? The owner said that that was all it needed, but I would think that pressure-washing would be damaging for it.

Thanks in advance for your experienced help!