Probably most of us have experienced this, or at least know it happening:http://badass-of-ne.forumotion.com/bad-talk-f5/good-morning-t2535.htm
I have replaced 2 that were about to break myself, and have seen 2 other broken ones firsthand.
Realizing that the coolant restrictors are becoming more fragile after this many years in service, T&M has been quietly moving towards production on a billet aluminum replacement.
They are machined out of solid bar stock with a hose barb at each end, and anodized black for protection & appearance. A fixed orifice to duplicate the intent of the design replaces the internal valve assembly and eliminates the moving parts.
Pricing hasn't been determined yet, but they will be reasonable alternative when compared to the GM replacements that are currently running about $22.00.
No pics yet, but I'll see if I can get some from them.
If you want one right away, just contact T&M through the info posed on F2Bkit.com.