Fiat hydraulic oil problem

Ok we had a leak on one of the pipes just off the hydraulic pump so I took the pipe off yesterday and got it fixed. Prior to that we were topping up the oil almost daily just to keep plenty in her and keep the hydraulics as a reasonable speed. Now yesterday before the pipe was taken off she did some work and I don't think there was much oil in her, from talking to the lad she was very slow on the loader. I put the pipe back in her last night and threw some new oil in but it's still incredibly slow. Now my question is would the filter be stuffed because she was ran so low?? Or when I changed the pipe would there be air in the system and is there some way of bleeding her?

As you can probably tell I haven't a clue!! It's a fiat 82-93, not exactly the fastest hydraulics in the world to begin with!

Thanks