now it wont start
 

Mine is a Ford 1991 7.3 IDI extended cab long bed XLT. I know it was a farm truck sold at auction to another farm, given to farmhand for pay, given to me to pay off debt. last owner knew NOTHING (actually less than that) about diesels. I drove it for 3 years without much problems. I did change the starter 5 times in 2 years the batteries once. When the return rail started leaking I got a repair kit pulled the injectors one at a time and cleaned them (did not dissemble the injectors) just soaked them in cleaner and reinstalled, replaced the return rail so now no leaks, hooked all lines back the way it was at first. Glow plugs stayed on for 2-3 seconds, checked and found 3 bad, replaced all 8 now wait to start light is on for 8-10 seconds but it will not start. Starter is slow again so I think I need to change the starter again. the only other thing I can think of is a air lock or air leak somewhere but I cannot find it. What should be the next move?:argh: