id be just taking the pump out and looking at that first to be honest as putting in new shells is pointless if the pump is at fault, al youl do is put new shells in it then cause damage to brand new ones if its the pump at fault.
to take the pump off, take the o/s/f wheel off, set the timing as thought you were doing a cambelt, support the engine with a jack under the sump (put a block off wood in between to stop damage) take the engine mount off, lower the engine down so that you can see it remove the cam belt, remove the bottom pulley, the oil pump ois held on by a series of 10mm bolts i think, well wotever size they are, remove these and the oil pump should come off,
if you dont know what it looks like look here:
http://cgi.ebay.co.uk/Ford-CVH-Oil-P...2em118Q2el1247

take it off an have a look! but fit a new gasket when you refit it, and it will make life a lot easier if you pack the rotor full of vasaliene as they can be a bit fo a pain to line back up again onto the keyway on the crank, but then drain a put fresh oil in the car once you have it sorted