Flexifit 406 glider strap attachment question

[lido14]

My glider strap on my flexit fit 406 mask broke. I have a replacement from an older mask that broke previously but I cannot slip the replacement strap into the slots on the mask. They won't fit in the slots despite how much pressure I'm exerting to push the strap in. Suggestions from anyone who has done a replacement would be appreciated. Thanks.