David are you indicating that what you are doing is safe? If so why? Are you doing it in a controlled environment?
I will say that what I do is safe from the standpoint that the mechanism will not be harmed. Exceptions: it will destroy rubber traction tires, so remove them first; it can also degrade some paints, so do not use it on locomotive shells. Heptane will only dissolve rubber-based residues, waxes and greases; it will not harm plastics.
I would not advocate that everyone use it in this manner, however. For myself, I have no qualms; I've been using solvents of all kinds for as long as I can remember. My father was a research chemist, and regularly brought home gallons of various solvents such as toluene, acetone, etc. (They used it for chromatography, and once used would be discarded as it had to be ultra-pure; so, he liberated it for use as paint thinner, cleaner, etc.) He taught me what solvents to use in which applications, as well as safe handling methods, from a very early age, so I liberally use solvents in ways that might alarm others.
As solvents go, heptane is relatively benign; at most it will cause mild dizziness when inhaled in high concentration, and it's non-poisonous (although still pretty nasty if ingested). Its greatest danger is that it will ignite explosively. To do this, however, it must be atomized in the presence of an open flame, so with care and good air circulation, it's quite safe to use indoors. I always have it on hand in a dispenser on my workbench; it's my go-to solvent 90% of the time. Hint: it's the ideal solvent to remove pesky price/UPC stickers, or any self-adhesive label that otherwise won't come off cleanly (Goo-Gone is nowhere near as good, and a lot nastier to smell).
Incidentally, I keep gallon containers of heptane, acetone, MEC and 90% alcohol on hand. Acetone is a good general all-purpose solvent for removing paint, cleaning brushes, and also debonding cyanoacrylate. I use MEC as a styrene bonding agent--significantly cheaper than any commercial plastic bonding agent. Alcohol is a decent paint stripper; I also use it as a hand and surface cleaner when working with resins.
