Whatever you do don't let nitromors, or any of the own brand equivalents, anywhere near plastic of any description.
As dbclass50 says one of my favourites is brake fluid, but some of the modern synthetics don't seem as good. Brake fluid does no damage to plastics at all (hence the plastic reservoir on modern cars). Care should be taken with skin as it is not very friendly.
Microstrip is a good product but owing to it's chemical nature can not be sent via the postal system, however most good model shops stock it at around £5-6 a pot.
Hope this helps.