i've done one or two i use a 5 ton hydrolic puller, i wd40 and give the sides of the drop arm a good wack with the lump hammer then put the puller on as tite as i can get it, ( then have been known to leave over night with puller on) then try to get puller up a bit titer then with a meter long punch and big lump hammer hit the drop arm from the engine bay( i've got a 200tdi with no fan cowling)
it can work if by hitting the drop arm (ball joint end) with a sledge but this can brake the arm
i've only once not mannaged to get it off after the seals went pop on the puller