O> On the other hand, one is tempted by a copy of the Colmar Ruckers by 
a
> Famous Maker. The base price of this instrument is $50,000 US, 

no instrument is worth that much, bar none, much less without a stand 
etc.
Anybody who pays that much....
Ian Pleeth got his original Transuntino for much less. 
BTW Ruckers do not have leathered slides.

> On the one recording I
> have, it comes so close to the sound of the original that I would easily be
> fooled if I didn't know it was a copy. 

recording are not trutsworthy anyway

However, I have heard rumors that
> this maker's instruments are sometimes subject to considerable structural
> instability.

Only rumors? 
 
> If I lived close to such a maker and felt assured that he would stand by his
> instruments,

That is a VERY BIG if!

OTOH, any responsible and honest builder will stand by his instruments.
I will and I know John Phillips or Owen or Mike Johnson or Hendrik do...


b