Hi! Can anyone help? I have an 18.2 cu ft reefer that had a horendous smell-- it had been turned off with rotten stuff inside. I have cleaned it thoroughly with bleach, antibacterial cleaner and baking soda but it retains a slight odor which I think may be coming from the styrofoam "diffuser" blocks in the panel in the top of the fridge compartment. They may have absorbed the odor. Is this possible and would replacing them help? Are they difficult to replace? Any other suggestions to eliminate the lingering smell would be greatly appreciated! Thanks.

Here your parts
Replacement parts for FRG FRT18KG3CW0 | AppliancePartsPros.com
Items 12 & 13 in the 4 Shelves section.

Here is a parts breakdown which should help you take it apart
ftp://ftp.electrolux-na.com/Pr.../Anderson/5995388468.pdf

but it retains a slight odor which I think may be coming from the styrofoam "diffuser" blocks in the panel in the top of the fridge compartment. They may have absorbed the odor. Is this possible and would replacing them help?
It is possible but without being there cannot say for sure. Did you flush some of the 10% bleach solution down the drain. White styrofoam will absorb odors as it is open cell. Soaking them in a 10% bleach solution should get rid of it as they will also absorb the bleach solution.
Also did you clean the drip tray under the unit and flush the defrost drain with the leach solution? Smells from the drip tray would apply if you can smell it with the doors closed especcially if it is stronger when the compressor is running.

Are they difficult to replace?
Not that difficult see the above parts breakdown. If possible you only want to drop it enough so you can replace the parts so that nothing is pulled loose.

Any other suggestions to eliminate the lingering smell would be greatly appreciated!
Putting the unit outside in the hot sun with the doors open for a couple days often can get rid of smells. Just have to be sure that a kid cannot climb inside. Leaving all the racks etc. in should discourage this. Also tying the doors open.

Sometimes no matter what you do the smell will linger for a long time!!!

THE ONLY thing that I have found that will work is FRESH GROUND COFFEE, spread some on a dish and put it in both sections, leave it 3 days and repeat again!!!! This should take care of it!!!!!!!:)