I have a similar problem at similar hours. The swing works for the first couple of minutes and then slows to a stop. The service manual says it could be several things including the swing brake or valves. Somone else here on a 447 reported a similar issue and it ended up being a piston seal...
Im new here and to excavators. Im an Australian residential builder pushing 50, slightly balding and my belly isn't getting any smaller.
I purchased a Toyota SDK4 20 years ago and she a beauty I have only done 800hrs on it so, I'm far from an expert.
I recently purchased a bobcat 337...