Problem with 25-50mm f/4 Nikkor

[kayeu]

I bought this lens off ebay and I started having problems with the focus not adjusting at all when I turned the focusing ring. I "solved" the problem by taking the lens off the camera and putting it back on. It would work for a while but then it would start happening again. Eventually I realised why... the section of the lens just below the focusing ring and just above the serrated silver ring in front of the aperture ring was popping out of place at one point. Any pressure on this point and it pops out. It's easy to click back into place. Taking it off the camera and put it back on was "fixing" it because I was inadvertently pushing it back into place.

The lens is performing fine when it's properly in place.

How difficult and expensive is this to repair? Does it have to be repaired? Will it lead to damage if it isn't?

I have emailed the seller to inform them of the problem but I haven't decided yet what to do.