The steps between weight and manufactures are not linear. Basically the step from 20 to 25 is not the same as the step from 25 to 30. The WT numbers don't correlate to anything, except one another. They are just numbers picked out of the sky. Losi 25 wt is thicker than Losi 20 weight, and that is about all you can guarantee. Ambient tempurature also has an effect on the oil as well. Like Blue Screw posted, your best bet for accuracy is to stick with a single brand. Or switch over to an oil that is CST rated. CST or centistrokes, is an actual measurment of fluid viscosity, so as long as an oil is accurately labeled, you could in theory switch between any CST measured oil and it should yield the same handling characteristics. Now it is possible that different brands of oil, wheather labeled WT or CST, would respond differently to temperature. Like was stated earlier, the absolute best thing is to pick one brand and stay with that. Losi is nice because it is certified and colored. AE is now made by Lucas, so it is probably also very consistant. A couple drops of food coloring would make the AE oils easier to identify if you are not very good at remembering what you have in your shocks.