hey, my '98 SD above 2000revs has a hissing noise like im losing boost!! theres also quite a lot of "warm"/fresh oil just above the turbo, around the inlet manifold and running round the back of the engine!! i thought the hissing was my lack of an airfilter (!!!!), but i got a new one and no difference!! i changed the turbo 8months ago when i changed the engine an it seems to be boosting fine?? any1 find this familiar??