The saga continues....
Returned to village PO, clutching the Royal Mail letter regarding samples (see above) for a 3rd attempt.
The atmosphere was tense as he read the letter; smoke trickled from both ears. Very reluctantly it was accepted, postage paid, no apologies.
Success was short-lived.
An hour later I was called on an ex-directory tel. no. (wtf?) with the PO guy cackling with revenge. He had called whoever he calls and was advised the letter (Royal Mail Chairman's Office) wasn't acceptable - it was (a) out of date (2013) and (b) "the rules have changed. If he let it go it would have to be taken out and destroyed. Remember, the Post Office has nothing to do with Royal Mail"
So 15-All until Monday when I research further.
Blackstone just emailed. They contacted Royal Mail a couple of years ago and got this reply:
As long as the oil samples are under a litre in volume and well packaged and placed in a leak-proof liner such as a sealed polythene bag, surrounded with absorbent material such as newspaper and sufficient cushioning material to protect each item from damage, that is all that is required. (Should the samples be in glass bottles, the package should also be marked as 'fragile'.) Your UK customers should also have a sender's address in the UK clearly visible on the outer packaging. More information and advice can be found on the Royal Mail website at the following link: http://www.royalmail.com/personal/help- ... -packaging I complied with the conditions in that link for my 3rd attempt.
The US destination isn't part of the equation - same for the UK, according to the Dangerous Good dept. of Royal Mail - all engine oil now classified as environmental waste ('phoned this morning) and won't be accepted.