Hello Matt:

From your post I gather you moved fuel injectors around but changed only one O-ring that broke. I recommend you change all injector O-rings and caps to avoid any vacuum leaks anytime you remove an injector. Complete Borg Warner kits are about $2 for each injector at Pep Boys. These worked well for me. Volvo sells its own kit for more money. Use lubricant to put injectors with new O-rings back in place. Some have recommend silicone and others petroleum jelly. Others warn of problems if you use either of these lubricants, like harm to O2 sensor from silicone. I have not experienced problems when in my ignorance I used petroleum jelly once and silicone lubricant another, but I cannot tell you more. You will want to read 700/900 FAQ. Do, however, change all O-rings to avoid any vacuum leaks. Best regards.