The B40 is a TX 200 clone and as such breech seals and piston seals are available at Air Rifle Headquarts.The breech seal on a TX 20 consists of two O rings, one on top of the other. You will find the O rings in the Lowe's or Home Depot plumbing department work fin in a pinch - or even long term.
not the same seal. call mike at flying dragon... he may be able to help. as per the cocking effort... about 30 lbs. mine is tuned and shoots about 17 fpe in .177. fantastic air rifle... shame they do not make it anymore.