kobelco sk21olc-6 slow bucket curl

[paradise pete]

Hello everyone, I have a kobelco sk210lc-6 excavator serial number: YQ08-U1955 ..Machine has 5800 hrs on meter. The machine seems to preforms all other functions well for its age. The problem is when you curl the bucket close it curls slow and you can hear a load "sssshhhhhhhhhh" coming from valve body. The bucket uncurls well even when your pushing something away with the bucket...Any ideas what this could be?

I have a friend with a 320C caterpillar with 3400hrs on meter that does the same thing, he rebuilt the bucket cylinder, that did make the problem lessen but it was still there...