in need of help !!!

hows it going ? i just wanted to put a few things down. i bought a discovery last year and ran into some problems soon after i bought it. since, it has been in my garage and moved around occasionally. my major problem now being winter is almost over and i have the time to mess around w/ it is a oil leak. the "rear cam bore seal" popped out and i have to remove the trans and flywheel to replace it. i need to know if anyone knows what causes this. if there is a tech here let me know. i haven`t called the dealership yet this week in fear of them just b.s.ing and telling me i have to bring it in. i`m A.S.E. certified i don`t work at a shop presently and don`t have one of my own, but i have one to use. i`m trying to get a shopmanual but it seams they are quite hard to get a hold of. if anyone knows anything about replacing this seal and what causes it to pop out(i.e. timing chain needs replacement, valvetrain movement, etc.) let me know...