You have to take off the push nuts, but you will have to replace them.
The
little tikes gearbox assembly can be purchased at this site http://www.shopjandl.com/
but if you just need the push nuts like I did you get them here http://www.shopjandl.com/0801-0226.html.
I had the same problem, so all I had to do has tighten up those screws and replace the push nuts.
Hope this helps