It'd put extra tension on the closer, but if it's a 2 part mechanism perhaps print a new 3D slider block for the latch?

(or test with a thin balsa kicker behind it to see if it seals more)

Is the window true? 

Could be closing at the top OK and not at the bottom frame

The catches are the turn handles without that silly flap thing the older ones have.

The handle on the right is quite tight as you close it, the one on the left not so much. There is a fair bit of wind noise in the left bottom corner and if you grasp the handle and pull it towards you when it is closed, the wind noise disappears completely.

I imagine it just needs adjusting somewhere but I am not sure which bit to adjust!

So like one of these?

I expect if it has the 2 part latch plate, you can replace or get someone to print another with more thickness. Would simulate pulling it tighter

Are you running windows 95 or XP? ;P

Geektastic: One of the top hung windows needs to be made to pull more slightly more tightly against the seals when closed. Does anyone know how you do that?

Thanks.

I've temporarily kludged it with a bit of packing foam under the close tab but will ring a glazier and see if I can get a less Heath Robinson solution!

I removed the catch today and found the issue.

The metal tab that closes against the frame has a plastic insert that contacts the frame. Insert is missing, presumed dead.

New rubber seals will also help...

see "exceed . co . nz" for an idea or three....