What about Buna O-Rings?
Buna is one of the most widely used O-Ring elastomer compounds. The others are Ethylene Propylene(EPR), Fluorocarbon(FKM), and Silicone(VMQ). There are many others, but not as common.
Buna is a Nitrile compound. The actual name is Acrylonitrile-Butadiene and can be referred to as Buna, Nitrile or NBR. Standard durometer, or hardness, is 70 or 90, but can be made in other durometers, and comes in Black. The temperature range is generally -30-degrees to 250-degrees. These are the least expensive and most readily available. Buna comes in standard and metric sizes.
Recommended use of Buna is with silicone greases and oils, water, petroleum oils and fuels.
Buna is not recommended for ketones, halogenated hydrocarbons, auto and aircraft glycol-based brake fluids, strong acids, and is not resistant to sunlight, ozone or weathering.
Buna has good wear resistance, good compression set resistance, good short-term resilience and good permeation resistance. It is used with hydraulic oils and fuels, extreme service, pneumatic and vacuum applications.