First thing i would try is to take the heat syncs off and clean them with some artic clean and put new thermal past on the cpu and gpu and bend the x-clamps... to make sure there is enough pressure... on the heat syncs... being you had a roach problem they are messy things, and stick like
... I doubt you will ever get the smell out of the xbox no matter what you use. but i would try that ... hopefully it cures the issue and doesn't need a reflow... or on its way to needing a reball....
that is what i would try 1st...
I dont do Roaches... Yuk!! hopefully you got rid of them and killed everything good luck let us know what the results are.