Part vs. Whole

It appears that I need to purchase a new furnace.  Actually I have a choice to make.  There is a part that has cracks in it allowing gas to seep in to our home.  That piece is still under warranty but for only one more year.  (My home is 9 years old.)  I can have this piece replaced for labor only, which is estimated at $1,200.  Or I can opt for a new furnace for approximately $3,000.

There are pros and cons to both.  If I opt to replace the piece it could be a cheaper option that could last for years.  However, I could replace the piece and it could crack again in a year and I'm having to replace it again or something else breaks and I'm having to spend $3,000 for a new furnace now.

If I opt to put in a whole new furnace it is really expensive, but it will likely come with a warranty for several years and I will not have to worry about it for some time (or so I hope).  Plus depending on which one I purchase I could be eligible for tax credits at the end of the year.  But it is approximately $3,000.

Ugh....when it rains it pours...any thoughts are appreciated.