Please help cat 315 slow hydraulics

Hello i need help i have a 1995 315 with arround 14,000 hours no major repairs on it. some times the machine is very very slow in all of its functions, but y lift the arm up and down and then it Works fine, and it Works fine all day, machine becomes slow like 2 or 3 times a day but i do the same thinks with the arm and Works fine again, any ideas of what can it be?

thanks i hope someone can help me on this

thanks
Mauricio

Please help cat 315 slow hydraulics