I use stag wellseal:
Developed by Rolls Royce Ltd and manufactured under license, this compound is the complete answer to sealing problems on machined faces.
Stag Wellseal jointing compound is non-flammable, has easy partability and is non-hardening it is formulated to give the best possible sealing
performance under a wide variety of conditions.
It can be used to seal threaded connections as well as flat- faced joints and can be used with or without a gasket, depending upon the design of the assembly.
Stag Wellseal Jointing Compound is highly resistant to the majority of commonly
used field, lubricants and coolants and is non-corrosive and free from
abrasive fillers.
Wellseal will withstand temperatures up to 195?C (383?F)
Oil or Coolant, machined surfaces.
for non-machined surfaces I use Super RTV Silicone, Fuel resistant and oil resistant so safe to use on inlets.
