O-rings compatible with:

Mineral oil:

• NBR (nitrile/buna-n)
• PTFE, AU, FKM (fluorine green color)
• VQM silicone (maybe, 10-20% swell)
  

DOT5.1 brake fluid (DOT3, DOT4):

• EPDM
• SBR
• PTFE, FKM
  

Synthetic based hydraulic oils:

• EPDM
• SBR
  

Source:

• https://www.marcorubber.com/o-ring-chemical-compatibility-chart.htm

• https://www.parker.com/Literature/O-Ring%20Division%20Literature/ORD%205700.pdf

Brakes that use:

• Mineral oil: Shimano, Tektro (Giant),

• DOT5.1: SRAM