Nissan Repair: seals behind timing cover, timing chain cover, piston rings

Question
i have an 1994 xe nissian sentra for my daughter,it leaks oil,its coming from behind timing chain cover,timing chain is good,been replaced before i got it 3 months ago,but seal went bad,i bought a book,is it something very hard to change,i know its time comsuming,do i have to remove the head off,or just loosen and remove bolts on one side of head?

Answer
The timing cover is not too much fun to remove and then there is the oil pan that will have to be resealed too.  Also, there is the front seal that is another source of leakage.  So, first identify the source and then, if you have the time, and tools you will be in for an experience.  There is another situation that needs to be discussed and that is blowby gas.  If the rings are going and additional pressure is building in the crankcase there could be a possibility that this is causing the seals to allow leaks.  So, do a compression check too.  From what you wrote the car was  a recent acquisition and the previous owner had the work done on the chain and cover?  Anyway, check to make sure you can get the leak to go away without replacement of the piston rings.  If you get to that point you might be looking at another engine or car.