I'm no hydraulics expert, but I've been around a few and asked advice from several. What I've always heard is no hydraulic system works as well hot as it does cold, there is a lot of expansion and contraction happens within the components. On average, the more often the temperatures cycle from high to low, and the more often it is operated when hot or cold, the shorter the lifespan of the components. What was recommended to me for prolonging these components was to never operate under load until at operating temps, always let it warm up before starting as this lets everything properly expand so things aren't too tight and creating additional wear. Don't run the system at high load for prolonged periods of time, allow plenty of idle and low load time during and between operations for the system to stay cool. CUT hydraulic systems aren't as robust as commercial duty skid steers and loaders. Once complete, don't just shut the system down, idle it and allow the circulating fluid to help cool down the system. I was told to look for something with a lot of flow and a large reservoir if doing a lot of hydraulic operations. Both, high flow rate and high fluid capacity help maintain steady temperatures over longer periods of work.
In short, heat could be the issue, or the heat may be revealing early warning signs of some upcoming failure.
