Thick window gasket replacement

[Akustik]

My double glazing windows have huge gaps in the corners where the gaskets have shrunk and need to be replaced. The gap between the window and the frame is broad, so I'm having trouble finding a replacement gasket.

The only one that's somewhat near the size I need is this one - https://www.ebay.co.uk/itm/110744374238

Last year, I ordered some of that gasket from eBay (enough for one small window) and while it does fit, it's on the small side. If I press hard enough it goes in the gap, which I think means it's not wide enough ... or is it actually fine to just be big enough to barely stay on? Will this affect the insulation it provides?

Does anyone know where I can find a replacement similar to the one I have currently (see image attached)?

 

[Wayners]

Sounds like the glass was made too narrow.

 

[crank39]

Googled 9mm wedge gasket and my first result

Wedge Gasket 9mm

 

[Akustik]

The 9mm I've indicated on the picture does not account for the little flaps which also add thickness.
I've contacted several companies which have sent me some samples and none of them have been thick enough except for one which was so thick I couldn't push it in.
Can anyone suggest any companies which manufacture window wedge gaskets that I can then contact to see if they have anything sufficiently thick?

As for the window thickness, I can't really say - the window does seem thicker than normal windows. I think the issue is whoever installed this has put really thin gaskets on the outside and really thick ones on the inside. It's a block of flats, so I'm hesitant about replacing the outside gaskets. Plus I probably wouldn't be able to so I'd have to pay someone to do it. And even then I don't know if they can move the window closer to the inside to allow for even gaskets on both sides.