I sent an e-mail to Nye lubricants asking if you could safely use Nye 759G gel on rubber, i.e o-rings. (Thus avoiding the cost of both 759G AND 779zc) They replied:
<font size="2" face="Verdana, Arial">So what type of rubber are SureFire O-rings made of? Does any one know?It depends on what type of rubber you are using. I've attached a compatibility chart that might help you. The 759G has a medium viscosity base oil which may not have as big an effect on the rubber as a lower viscosity base oil.