Right, it's not made to stand up to the heat that you'll have in your mash and you may get off flavors, from the lead or solvents inside. Again, it's such a small piece that it may not make much difference, but the fact is nobody knows. It's your beer, so feel free to give it a try and see. If it tastes solvent-like, you'll know why.
This group of flavors is very similar to the alcohol and ester flavors, but are harsher to the tongue. These flavors often result from a combination of high fermentation temperatures and oxidation. They can also be leached from cheap plastic brewing equipment or if PVC tubing is used as a lautering manifold material. The solvents in some plastics like PVC can be leached by high temperatures.