The perfect remedy for this is to use oil seal materials that are rated for the temperature of your application. Also, ensure that the elastomer is free from volatile constituents like waxes, plasticizers, etc.

Types Of Oil Additives

Acrylic rubber (ACM)

Modern engine oils, such as the current SG classification for gasoline engines, contain a large fraction of additives, many of which are detrimental to fluoroelastomers. The primary functions of oil-additive packages are to protect metal parts, avoid deposits in the engine, minimize oil degradation, and adjust fluid viscosity. Little attention has been paid to avoiding damage to rubber seals. Instead, elastomer producers have been expected to provide new, higher-performing products at no increased cost to auto manufacturers. Among the additives with moieties that may attack fluoroelastomers at high temperature are detergents (phenolates), dispersants (succinimides, alkylphenol amines), and antioxidants (amines, sulfides, hindered phenols).⁴ Many of these components are multifunctional, containing phenol or amine groups that can dehydrofluorinate and crosslink VDF-containing fluoroelastomers, leading to loss of elongation and eventual embrittlement. However, the rate and extent of reactions with seals are affected by many factors, including whether air is present in the system. When oil is exposed to air at high temperature, additives may undergo considerable changes. For example, a significant fraction of amines may be oxidized to amides, which have little effect on fluoroelastomers.⁵

The main benefits of Nitrile when opting for use as an oil seal includes: 

In these instances, Viton can be the perfect sealing material for methanol/ethanol-blended gasoline. 

When there is a need for rebuilding a cylinder and pump instead of building a new one.