Steve, just found this on eBay. Complete seal kit for s310. Less than a tenner. Just so you know if gun shop try to charge too much. Link below.
http://http://cgi.ebay.co.uk/AIR-ARMS-S310-S400-S410-SEAL-KIT-Crinkle-Washers-/320577463065?pt=UK_SportingGoods_Hunting_ShootingSports_ET&hash=item4aa3e7e319#ht_918wt_920
http://http://cgi.ebay.co.uk/AIR-ARMS-S310-S400-S410-SEAL-KIT-Crinkle-Washers-/320577463065?pt=UK_SportingGoods_Hunting_ShootingSports_ET&hash=item4aa3e7e319#ht_918wt_920