Supercharger leaking oil

[Optimiser]

Hi all,
During my first session at a recent track day I was getting oil leaking out of the breather valve on my Rotrex supercharger. I'm thinking it's because I'm over spinning with pulley upgrades as it didn't leak at a previous track day when the pulleys were stock. It doesn't leak at all driving on the road. It's just leaks at constant high RPM.
Is there any fix for this other than "downgrading" the pulleys which I don't want to do. Would getting a "Trim" upgrade with the high speed bearings and impeller fix this?
Has anyone else experienced this at the track with an "over spinning" Rotrex supercharger?
The only possible solution I could find on the net was to reduce the oil level in the supercharger by 1/4 to 1/2 oz out of it's normal 4 oz max fill, but I've not tried that yet.