My keyboard bezel now has that extra flex and an extra clunk sound effect while pressing keys h y u k l . space m n

Mines level all the way accross no issues. Think the later build N900s have had the issue address with the keyboard? the bottom plastic line to be fair does move but i have to purposely try and move it for it to be an issue.

Just post the link up to the spare parts ordering website on here? might be worthwhile replacing the keyboard with a new one / or frame if they are cheap.

Might be good to just have a spare anyway i see these keyboards wearing out after a few years use !

On mine the frame has no gap but makes clicking sounds when pressed after leaving the phone without use for a while. I noticed this right after unboxing the devise...I cant send it back to nokia for a few clicking sounds which are so infrequent, although they are because of the keyboards loose frame.

mine shows this gap, too.
according to the service manual the replacement procedure takes untightening the torque screws and levelling the keyboard cover (!! only the cover where the gap appears !!) slightly up until it snaps off.

it is held by clips. i think those are getting lose from normal use / force.
replacement part is about 9,99 €. i'll keep it this way and wait till it gets worse before i'll try to replace it. but it's good to know that it's only the cover and not the whole keyboard

Mine has a crack and I want to replace the keyboard frame. Can I do it without disassembling the device?

I doubt it, you need to watch a video on youtube on how to take it apart