Just replaced the T piece on my 2012 2.0 Duratec, with this:
http://www.cbsonline.co.uk/product/Brass_Tee_19mm_BTEE19
The good news is that the Caterham part I took off seems to be this:
http://www.caterhamparts.co.uk/product.php?id_product=4299
and seems rather good - very thick walled, and apparently pretty strong, rather than the smaller part found on Duncan's Sigma.
So, perhaps those of us with the larger 19mm part need not worry? But, I'm happy that I now have a metal part in place, none the less. Thanks for the tip.