bluskis
I except what you say about turning the prop backwards damaging a vac pump but only if it is worn almost to the point at which it is about to fail.
The carbon vanes in the pump are so lightly loaded at the speeds that you can turn the prop by hand that I cannot see how any damage could take place except if the vane had excecive play in the rotor IE a high time pump. I can see how damage could be done if the pump was run at high speed backwards.
The latest pumps on the market have an inspection port to monitor vane condition this should put the end to the lie that " the pump failed because it was turned bacwards " when the engineers remove pumps with worn vanes before the pump fails.
I suspect the warning that came with your new pump is due to smart thinking on the part of the pump maker in using this bit of aviation folklore to keep the warranty clames down and to muddy the waters in case of leagal action after a pump failure , now that it is posable to see inside a pump and check the state of the vanes i see the truth coming out.
What I dont see is this disappering from the folklore quickly after all only last week I was told that the engine in a PA28 should not be leaned below 5000 ft ( this is a tiger moth limitation ) .........................it never fails to amuse me how these things become folklore !!!.