Just going back to the original question.
The aeroplane is syndicate owned - they have one or more trusted people who are co-owners (most likely) whose flying standards and judgement are known and accepted to be of an acceptable standard for that group.
A new member joins - who until proven otherwise is an unknown quantity. He wants to use an instructor who is also an unknown quantity.
Legalities here to me are pretty much secondary - the syndicate has every right and reason to make sure that anybody flying their aeroplane meets their acceptable standards. And also if this 17,000hr instructor is both good and has a good level of professional humility - he'll have absolutely no issue with being checked out by a PPL who knows the aeroplane well, and hopefully it won't take very long at-all.
So, myself, I think that there is no issue here - just do it. Fighting the requirement just indicates to the syndicate an unprofessional attitude towards flying the aeroplane, and that's no way to start off as a new member.
G