Getting my patrol 1991 GQY60 in good nick

[the evil twin]

Since that big hose runs into the air filter, I suppose I should get a new air filter too. Any recommendations? The manual says there are two types, one which must be cleaned occasionally and one which must be replaced occasionally.

Thanks,
Paddy

The 'first' is a cyclone style pre-cleaner, that should just need a clean every now and then depending on conditions.
The 'second' is a standard type of air filter at the Carby, that one is normally paper style and can't be cleaned and should need replacement when dirty.
I don't replace filters on a 'klm's travelled' or 'time' basis I clean or replace them on inspection IE it depends on the filter and it depends on whether there has been a lot of dusty roads/terrain.