Boeing is only questionable responsible in any case since the planes in question were all built under McDonnel Douglas when it was its own company prior to the boeing merge. And the service life question is all kinds of up in the air the inital 4000 hour life is past on pretty much all but the least used 15's but about 1/3rd of the way through delivery that was upped to 16,000 hours based on what was then being flown (lots of ferrying and training missions) according to the manufactorer. In the 90's the AF said 8,000 and it pretty much comes down to is the plane being used mainly in combat missions and combat traing which really stress a plane or is it getting most of its hours flight training and ferrying which are maybe 1/3rd as stressful. All e's for their bomb carring duties have a beefier frame and are rated at 16,000 with 70% being combat hours. Earlier models are almost on a plane by plane basis with its logs of combat hours being the imporatnt question as to how severely stressed it is. There is a decent article about it on global security
F-15 Eagle but its a fair ammount of reading for realitively little hard specifics will check and see if I can find anything publically availible from either Mc Douglas or Boeing or the AF.