I'd check the boot around the gear lever. Look for a tear or rip, or where it may have let go from the sides.
Being a 2008 model the aircon should be gassed with R134A which smells like paintball gun discharge (oddly enough because paintball guns use R134A as propellant). It's noticeable, unpleasant and should only happen when the aircon has been turned on. Just to make sure about that though, it might be an idea to have someone test for leaks. Take it for a half-hour drive and stop at an aircon engineer's workshop, who will be able to nail the smell if it's from your aircon.
Other than that, I suspect you're getting fumes in the cabin from around the gear lever. Its happened before.