If it is pure silicone you can use a lil to assist in installation. Not too much tho you dont want the rubber to swell and you dont want to get the oil on the inside of the rubber itll make the hop up not hop much at all. Most cases if h9u are doing it in the right order (rubber on barrel. Slide into hop unit. Reassemble hop arm and such with nub.) itll go the gether fine. Sometimes with a lil persuation.
Edit. Use this if you gotta
http://www.airsoftparts.ca/store2/in...roducts_id=623