The first problem results from the temperature of the oil, causing damge to the tissue but can recover in a couple of days. When this happens you need to put activated charcoal asap to prevent long term damage. You can usually find a good activated charcoal at a pool supply house, they use it in swimming pool filters. In defense of the operator it is not easy to detect when it first happens, it is almost invisiible but if 100% attention is used it should be detected. Many times this occurs when verticutting and that makes it even more difficult to detect. If it goers undetected for more then an hour or so,,,get ready to do some sod replacement. You can also buy a red dye to add to the hydraulic oil to aid in detection and I have heard of courses using an hydraulic oil used in food processing machinery that does less damage to turf. Little help for now but hopefully this will help for the future.