Weak steering Bobcat 743

[Minkhe]

I've got a Bobcat 743 from late 80s/early 90s with approx 2000h on the engine. It works perfect except from the steering. The steering works ok to the right but after a few minutes in operation it goes from normal to weak when I turn to left, no difference at idle or full speed. I appreciate if anyone have experiences of "how to do" to share. Another question - do anyone know where I can find a user manual and service/repair manual to this machine ? Thanks in advance !