freelander rear diff problem

hi am new member and just got my first freelander, which is a 98 2l diesel. i bought it on sunday 13th nov. brought it back home 350 mile trip no problems. yesterday noticed oil coming out of rear diff where the propshaft coupling goes in the diff. also there is a bit of play when you shake the prop shaft about, would anyone know what the problem woulb be. is it normal to be able to move shaft about by hand. if it is would it need a new oil seal. if its more sinister and i need a new diff can i fit any, or does it have to be from the same year as i have read that ratios changed on later models. thanks for your help.steve