Wayne:
Prochems red rx might work using the heat transfer method as described on the bottle. Have had some success in the past with this approach.
Tbh if the custy has tried the old 1001 on the stain then chances are it'll be permanent. Sometimes you can tell whether the custy has given it a go if the area around the stain has gone "Hairy" like its been scrubbed to death.
As a last resort I would use hydrogen peroxide on it but no more that 6% 20 volume. HP has a mild bleaching effect. It has no properties that will actually remove the stain. The stain will still be there but won't be as pronounced as hp will lightly bleach it.
Hydramaster also do a product called knock out. However I find it very expensive for what it is....2 bottles, one basically containing Hydrogen Peroxide and the other amonia. When mixed together according to Hydramaster their supposed to be the "Product to use when all else fails!!"
Tbh didn't find it any better than the hp you buy from boots at a fraction of the price!!
Good luck and remember explain to the customer that you may only have limited success. This way if you manage to remove the stain you'll be the dogs dangly bits
Will