Hi John, and welcome to the BBS -- particularly this here Collectors Corner section, as imo, this is the best bit of the BBS by a clear country mile . Your BSA Challenger is quite a sought after rifle, so selling it should raise you a fair few quid, maybe in the region of £200 +/- (difficult to give a spot-on valuation without photos).
If you do choose to renovate your BSA Challenger (Mercury variant), these people should have all the spares you may need: http://www.gunspares.co.uk/shopdispl...cat=Challenger, but should you choose to sell, do please start a fresh thread, with a price, as per the BBS rules as in the stickies etc: http://www.airgunbbs.com/showthread....luation-thread..
Should you wish to sell, you may place an advert in both this collectors section, and once you have accrued enough of a BBS presence (http://www.airgunbbs.com/showthread....sales-sections), in the main sales section, which you currently can not see, too. Further, if you do want to sell, it may be worth trying to post a set of photos of your Challenger here, via links to an external hosting site, and invite valuations to help guide you?
Hope all this helps, and once again, WELCOME to the Airgun BBS . Atb: G.