Intrigued by this discussion, I looked at the olympus supplied grease PSOLG-3 (for the PT-EP13 housing, but maybe for others too). It says "Silicone grease". It says "Silicone Grease, only for Silicone O-Ring". I assume there's some subtlty I'm missing, since it seems to contradict the above chart. Probably the name doesn't really tell much about the chemical composition.
There's no mileage in olympus or any other vendor helping you work out if a different grease will work for your o-rings and plenty of downside if they try to help and you misinterpret the advice and use the wrong material and cause the o-ring to swell. So you'll never get any other advice than "use our grease"