Silicone spray was applied to the felts at the factory. After 20-30 years, they will become dried out and lose their effectiveness - as well as tear or become dislodged due to non-lubricated friction. Application of a lubricant is neccessary to maintain good health of the piano to last the next 20-30 years.
As long as your escapement is set, double bounce will not be an issue - application of a moderate amount of lube to dry felts will not induce such a scenario to begin with. Going nutso with the lube may in fact cause such problems, though. So moderation is the key.
In older piano which have felts on the hammer cam and no bump on the pedestal, double bounce may be of more concern. Doing the key ped mod (which cradles the hammer cam on contact with the tine, as well as engages the hammer with less downward force) will certainly overcome the double bounce as it relates to lubrication. But again, knowing how to set perfect escapement is a must.
I personally use Food Grade Silicone (SprayOn S00210). It is easy to apply and spreads to other surfaces nicely. I give the ped felts a quick spray, and then one shot in each of the bushings. Then the keys should dry for about 10 minutes before being put back on the frame.
