The original chemical 'aroma' never went away despite hosing with all manner of detergents and disinfectant.
Quite a few years ago at a gliding comp, I was asked to get the QFE reading from the altimeter of one of the tugs (a Pawnee of course) to advise gliders on final glide on any change they should apply to their own altimeter setting. (long story here - I'll spare you the details). I dropped the door and poked my head inside the office to be greeted by the unmistakable 'aroma' of 2-4D Ester 80%. I was well familiar with it as the herbicide of choice for cruciform weeds in cereal crops and along with most farmers had used it myself. as the then primary attack against the most common and troublesome weeds. It must have been many years since this workhorse had been retired to glider towing, but the memories of its earlier lifetime persisted.
I commented on this to one of the tuggies - "Hell yes!" he said "they all smell like that!".