Hi CMAC,

give Pete a ring on 07970598116, he's the service manager for ACE, there's not many who know as much as him on Hitachi screws, as well as the chillers. He may be able to assist and no doubt carry out any necessary works. He also has at hand experienced and competant engineers for these compressors and chillers.
Hope this helps
PS The only gaskets that would require replacement are for the suction or discharge pipe flanges, oil filter plate, suction bell end, discharge separator housing or the terminal plate, you shouldn't need to touch anything internally.
Care has to be taken when pressure testing, the terminal plate will only take upto 13Kg/cm2 or 20Kg/cm2 depending on the age.
If the oil is ester, please check, this needs to be replaced and the system sealed within one hour as th is hydroscopic. Oil ideally needs to be poured in via the discharge port of the oil separator