Si, pero no pone que sean precisamente las gomas. Puede que hayan dilataciones del metal o vete tu a saber.
STEM
The stem gasket needs to seal in a semi-dynamic environment. The winding of the crown will cause the sealing area to rub, so the gasket needs to withstand abrasion. In addition, in screw-down crowns, the upper seal needs to withstand numerous compressions and de-compressions and still remain springy, ie have good compression set properties. Resistance to hydrocarbons (fuel, oil etc) is not really that important, unless you regularly store your watch in gasoline. Similarly, resistance to UV, high temperatures (over 200 F), and ozone are not required for the following reasons: UV - watch gaskets are not stored or exposed to UV for extented periods of time, unlike the rubber seal around your car window, high temperatures, by high temperatures we are talking about 200F and above, and lastly ozone which affects the service life of the rubber, but generally speaking, all rubbers will last 10 to 20 years, unless you store your watch near a large ozone generator, such as a huge generator. We will look at gas impermeability and saturation diving later.
So, let's rank rubbers by their abrasion resistance and compression set qualities. There are more types of rubber than listed, but I won't get into them as other properties make them less important.
Ranked for abrasion resistance (E-excellent, G- good, A-average, F-fair, P-poor):
Chlorosulfonated polyethylene (CSPE) - E
Natural rubber (NR) - E
Polyurethane (AU/EU) - E
Styrene-butadiene (SBR) - G
Nitrile (NBR) - G
Fluorocarbon (FKM) - G
Ethylene-Propylene (EPDN) - G
Silicone (VMQ) - G
Ranked for compression set (E-excellent, G- good, A-average, F-fair, P-poor):
Chlorosulfonated polyethylene (CSPE) - E
Natural rubber (NR) - E
Nitrile (NBR) - E
Fluorocarbon (FKM) - E
Ethylene-Propylene (EDPN) - E
Silicone (VMQ) - G
Styrene-butadiene (SBR) - G
Polyurethane (AU/EU) - F
We can see from the above CSPE would be best, but fluorocarbon and silicone gaskets are the most common types of rubber used in making o-rings, so either of the two are adequate in top seal of a screw-down crown and fluorocarbon being slightly better were sliding is a factor.
CASE BACKS
Case backs see almost no dynamic action and few repeated compression cycles, so from the above natural rubber, another common o-ring material, would be better that fluorocarbon, as it resist water swelling and water penetration better than fluorocarbon (again, CPSE would be best).
All of these rubber swell to varying degrees when soaked in hydrocarbons, such and gasoline, oil or grease, but swelling goes away when the hydrocarbon evaporates off, CPSE and nitrile being the best in resisting, then fluorocarbon being good then silicone, average or fair.
SATURATION DIVING AND GAS IMPERMEABILITY
As most understand, Helium atoms will seep through the rubber, some are better than others in resisting this. Fluorocarbon is good at resisting this seepage but Styrene-butadiene and CPSE are equal if not better in some regards to gas penetration. One of these is probably the compound used by Seiko.
CONCLUSIONS
Silicone rubber is perfectly adequate in most watch gasket applications, with fluorocarbon slightly better. Fluorocarbon rubber is slightly more expensive, so I feel that its use is more along the logic of “we use 904 instead of 316 stainless,” ie, yes, there is an advantage in performance, at the cost of economy, but the advantage in marketability is sufficient to overcome this. In short, fluorocarbon gaskets are the best of the cheapest types of gaskets.
My opinions, your mileage may vary.
EDIT: The oil used in all of the oil-filled watches
is silicone oil, so it is basically the same stuff as the seal (if a silicone gasket) or completely compatible with all rubbers.
EDIT 2: Buna-N rubber is the tradename for nitrile (NBR) rubber. It is cheaper than Fluorocarbons (Viton) better at compression set and abrasion, but mot as good at resisting hydrocarbons, or high temperatures.