They have apparently assured themselves that the O ring material is OK - But I shall ask about that anyway.
I understand viton is a brand name - what is the actual material that is required?
Counter to this I found the following:
"High Viscosity Silicone Damping Fluids are particularly effective for use in instruments and gauge that will operate in a wide service temperature range (-40°C to 200°C). Silicone fluids are hydrophobic and prevent humidity from entering the gauge/instrument housing. This is very important. At low temperatures, water condensation can freeze and cause damage to the sensitive parts within the gauge/instrument housing. Ultimately, Silicone Damping Fluids will extend the service life of the equipment that it fills and provide more accurate readings even in the harshest of conditions.
Properties:
•Dampen vibration in gauges, instruments, meters and avionic instruments
•Protects internal components against vibration, freezing and corrosion.
•Extends service life of gauges, instruments, meters and avionic instruments.
•Wide service temperature range
•Low viscosity change at temperature (low V.T.C.)
•Inert to virtually all o-rings, gaskets, seals and valves *
•High Dielectric Strength
*not recommended for silicone rubber due to possibility of swelling"
Which would tend to indicate the damping fluid is not likely to damage the O rings.
Steve