I have been testing the Surfix for several months. The mini containers, or bulbs, are air tight containers when the screw on cap is secure. To use for oil application, you put on the green dispenser cap, but when done using, you put the original screw cap back on and the container is airtight. The oil has a in bulb shelf life similar to other linseed oil type products. It doesnt harden or evaporate in the sealed bulb. Also, the bulbs are small enough that you are likely to be using them up fairly quickly and the most practical method appears to be to use the 5 liter refill station with the screw on (to bulb) pump to keep refilling the smaller bulbs, and control the storage situation that way. Its an oil that shakes up well even after months of idle shelf time.
I am assuming that this is what the question was in reference to, shelf life in the bulb.
However, I have also seen others ask about how long the dispenser sponge lasts in the tin container after use. My recommendation on that is to use each applicator sponge for the series of steps for a project, storing inside the tin for the 6 hour in between coat wait period, then discard at the end of the project. The cost of replacement dispensor sponge applicators seems consistent with the approach of starting each project fresh with a new applicator, and they do get a little worn out after a couple of rounds. I don't consider the tin to be a long term wet oil storage solution, but its a handy overnighter to keep your applicator wet in between coats. All of this is cleaner and generally a better user experience than traditional oil rubbed wet rag handling.
Not sure what Festool's stance on that is, but that has been my observation.
