What to do about 1/2" NPT thread tapped out too wide?

I have an intake manifold with a 1/2 NPT port for a temp sensor. Old sensor was frozen solid (marine engine) so I drilled out the brass and ran a tap through it, but it was so corroded I had to drive the tap in pretty far (tapered thread) and now the threads are too wide for a 1/2 NPT temp sensor to fit snug enough to make a proper seal.

Not sure how I can fix this, but I would like to save the manifold if possible