My 88 IROC with the 350 TPI has developed a pretty strong leak from the metal return line labeled as the leftmost (2) on the below diagram. Where can I source once to replace it with?

 

You could check GM stock and see if they still have one or get one from a parts car.

 

Delete it and put a standard 2 port valve. Use a piece of hose for the return. Really cleans up the coolant routing. If you are really stuck on keeping the coolant bypass function for some un-known reason, use a 4-port valve for a 97 Suburban/Express Van. That metal pipe is nearly made of unobtanium and often ends up leaking because it rusts through as most if not all are thin steel rather than aluminum.

 

If you have a part number:

https://www.rearcounter.com/

https://www.partsvoice.com/

Good luck

 

Part number 14101549. Discontinued in 2010 and no stock on hand at any GM location. Parts car is the way to go.

 

If you get one off a parts car it will be just as rusted inside as your failed one. A temporary solution ONLY at best.

Don't bother with another steel one. It's quite easy to make one out of copper tubing, which will probably outlast the engine castings.

 

Roll some (hose) beads in the tube and you'll have a real trick replacement.