Hi Lavendula
I agree with you about Wintergreen being great in certain conditions and in particular blends.
The main reason we're told not to use the oil is because it is made up 98% of methyl salicylate - which is what is used to make asprin. Methyl salicylate is an natural anti-inflammatory and painkiller and can cause some major side effects and sensitivities in people. As with asprin, this oil should not be used by anyone who has stomach ulcers, is alergic to asprin or asprin based products, kidney problems, liver problems, on warfarin or other blood thinning meds, pregnant women, elderly, children or anyone with immune problems.
I would never use this at any level above 0.5% dilution in a topical blend or balm due to the sensitivity it can cause in some people.
You might find this website helpful: http://www.naha.org/articles/toxicity_myths.htm.
Also, Robert Tisserand's book about Essential oil safety is helpful.
There are very few people in the UK who sell Wintergreen oil at retail amounts. It can be purchased in kilo sizes as it's mostly used by large commercial and manufacturing companies. As with most non-aromatherapy muscle rubs and inhalation oils, they don't always use pure essential oils so even the wintergreen they use is not the "pure" stuff - and they also normally don't use oils in the same high levels that we aromatherapists would use. I presume that this is why oils that we are told are hazardous are still used commercially.
Did you find any other information about the oil?