I have worked in manufacturing plenty - and trust me, there is no chance there will be traces of one material on the machine when another is ran through it.
Even when talking woolmills - in "t'mill" we used to have to air hose the whole thing and get the 'fettlers'(guys with brushes!) in to scrape the wheel combs that spread the fibres of the wool, after each batch ran through it. Thoroughly.
Can you imagine a pharm company producing a product that has another compound in from manufacturing errors?
I can just picture this printed on drug labels now...
-packed in a factory which handles steroids-
may contain trenbolone
Seriously i can imagine that the factory where the large batches of drugs are made - say AAS - share the oil prep facilities for each product, but it splits off to deal with each individual chemical separately...