Do you have an Ali case? If so I had to clearance a little bit underneath my case as it slightly fouled on my empi 3.5 deep sump. This prevented the sump sitting perfectly flush with the case. May be worth a look
Lee
I had that problem too Lee but clearanced the sump to allow it to fit. My guess is its the gasket compressing that's causing it.
That's an uneducated guess though