As the ML article states, refortifying additives in turbine oils can be very complex. Other lubricants lend themselves to additive refortification much more than turbine oils. Adding anti-oxidants to turbine oils will have a positive result on RPVOT values, since this test is highly influenced with antioxidant formulations. Therefore, you may be able to reach 4-500 minutes. But, if the refortification is not done properly, the RPVOT value will quickly drop down once the oil is in service and a host of serious performance problems can occur (as outlined in the article.)
I'm aware of one oil company that used to sell an additive concentrate for turbine oils, but they no longer do as the risk for problems was too high. Adding a couple of drums to your system is not advisable, as the volume of your system may not be exactly known and additive refortification requires specific blending equipment.
If you are using an old Group I turbine oil, the refortifying process is simpler. Group II's are much more sensitive because of a lower solubility. Furthermore, some formulations use solid additives that are melted into the oil - not a simple task to perform on-site. Often times, the amount of up front analysis to confirm additive compatibility and performance is daunting and costly. This impacts the potential savings from additive refortification.
If you're still interested in refortifying your oil's additives, do a lot of research on the prospective contractor. Ask for several references and make sure that they have an in-depth understanding of the oil's formulation.
If I were in your shoes, I would simply follow ASTM 4378's recommendations of changing the oil when the RPVOT value hits 25% of new. Much less complicated!
