I have a 2008 CX-9 with a Drivers side seat that is loose. Took it to dealer and only way to fix is replace seat for $3100.00 (Ouch).
They said it was the Seat Rail assembly and there is no way to fix without replacing the seat. Looking for anyone who may have had a similar issue and possible work around or Fix.

 

I would try some local shops. Dealers don't like to weld,a competent mechanic could likely fix it. If not i would try salvage yards.