What does the manual say? (presumably supplied with the unit whether it was hired or not).
The reason I ask is that if the manual states Max8k psi then whether the unit is safe or not is not overly in doubt. If used to the stated pressure it should be deemed as safe.
If the manufacturers manual states pressures greater than 8kpsi then that is a safety issue and it needs addressing.
If there is no manual, and therefore no safety instructions, then that needs addressing also.
In any case…….
If the unit safe operating pressure has been knowingly exceeded which, by your own admission it has, then it should be taken out of service and sent back to base.