gear box slap or diff ?

ok i dont really know where the slap is but theres alot of play wen taking off anyone had this prob and whats the fix please

Most common reason on 200tdi's and early 300tdi's is because due to lack of lubrification the main cog in the transfer box that takes the drive from the gearbox shags the splines on the shaft!

This was solved by new cog with holes drilled in it to let oil through.But if yeh shaft is fooked it's too late!