adding a small amount more of softener should not add more chemical smell than it already has.
also,
back when I was racing slot cars in HOPRA & UFHORA
the chassis on the race cars were plastic
if we boiled them they would get softer
if we baked them they would get stiffer
it was different plastic than worm plastisol but mite be
kinda where the hot water comes in ?
I have had hand poured sticks with heavy salt that got
firm after setting around , I boiled a few for 10 minutes, they were much
softer after that, its been a while so I do not remember how long they stayed soft .