GM P/N 25055272 No Longer Available (NLA)
AC Delco TS1012 Discontinued

From all of the comments here and on other Diesel sites, I'm concerned that one of these is a necessity.
I looked all over the web, Rock Auto, AutoZone, JEGs, etc. (JEGs sold me one, then had to tell me a week later that they were NLA) I then did just plain old Google searches. Found dozens of places that listed them, but when queried, all came back with the same answer.... No Longer Available.
$20 seemed to be the original price when they were available.
I found one place on Amazon that had one, pd $37.70 for it. It has been shipped. Now that it has been shipped, that supplier shows "Not Available" for this part, so I must have purchased the last one. We sill see in a few days if I really get the real thing.
I'll let you know....