Same problem here. the spring attaches to the metal pin on the inside and another metal pin holds it closed I got a spring from RS. Click and paste
http://rswww.com/cgi-bin/bv/rswww/searchBrowseAction.do?Nr=AND(avl%3auk,searchDiscon_uk%3aN)&Ntx=mode%20matchpartial&N=4294731262&in_dim_search=1&name=SiteStandard&forwardingPage=line&R=0684406&callingPage=/jsp/search/search.jsp&BV_SessionID=@@@@0091747845.1181593600@@@@&BV_EngineID=ccdhaddlegjikddcefeceeldgondhgj.0&cacheID=ukie
Hope this helps.
Ninjaneil
June 2007