Tractor hydraulic fitting was leaking today, o-ring had torn. I found one in my parts bin that fit but no idea what type of material. Are hydraulic o-rings unique that I should replace?

I have a Troy Built string trimmer TB32EC. The bump head quit turning after wrapping it in some tall grass. I unwrapped the grass. With the engine running, now the head will not turn, even with no load. Yet the head turns easy by hand. I figured the clutch had gone bad. So I removed the clutch to order a new one. However, after removing the engine fro the shaft. I noticed that when I turn the shaft by hand. The head will not move. When I turn the head by hand, the shaft does not move? Is this normal. Or is the shaft maybe broken or damaged? Is there something else I should check? This all new ground for me. Hate to order a new clutch I don't need. Thanks in advance.