Duct Tape.

I took my out a cleaned it really well with alcohol, it had a couple of cracks in the center and on the sides, that created that diesel smell in the back.

So I duct taped it. And it's been about a year with no smell...Not perfect but better than speeding a hundred bucks...

Oh and don't even bother going to a junkyard to find one of these things...I check atleast three car and all have been cracked.

Jason