Aliphatic petroleum distillate covers a wide range of materials, straight chain hydrocarbons of different molecular weight ranges. Usually flushes use relatively low molecular weight fractions for lower viscosity and slightly better solvency. They do not have enough solvency to harm the seals formulated to withstand their higher molecular weight brothers, dino oil. What you need to watch are alcohols, esters, ketones and other polar materials. Aromatics, benzene, toluene, xylene are hard on elastomers too. It is a balance between being polar enough to clean the materials the non polar oil leaves behind, and not polar enough to harm the rubber made polar enough to resist the non polar oil.
