PetroStreet

How frequent a leak from a valve gland should be considered as acceptable?
Same valve having gland leaks in 5 to 6 years... should that be considered as a bad actor?

I would recommend to treat this subject based upon the criticality.
The valves in critical services should be studied with the recommendations provided in the manual, OEM supplied documentation. There are instances where the mention of gland servicing is clearly available and is required to be followed as-is; which most of the maintenance groups do not plan. Most of the maintenance performed is on corrective side or to have emissions /specialized surveys /data analysis (maintenance record based) to plan during the available outages to perform preventive maintenance or fix which was temporarily addressed during operation.

There is no petrochemical unit free of valve gland leaks but something which is persistent, happening every 2 to 3 years indicate an issue.
But a leak happening in 5-6 hours may not be a problem as we experience.
Still I understand collection of data, and consulting OEM (if available) is a good idea.
In case of no OEM support available for the valve, it is recommended to carefully assess the leak data and identify the issues systematically supported with a formal RCA involving all concerned.

Useful inputs, all.