Universal Oil

I have 4 2 cycle devices, 2=40:1 and 2=50:1. My problem is I do not use enough of either to mix up 2 separate gallons. My Sthil dealer sold me some universal oil that should work with anything to 50:1, but the 40:1 trimmer does not seem to like it as well. Any suggestions? Would the 40:1 work in my Sthil chain saw and Ryobi trimmer? I use good quality alcohol free gas for the mix. A gallon will last all Summer. I have a chain saw, 2 trimmers, and a mini tiller. I a perfect I would get Sthil brand everything.