Too Good to be true? 1997 Ford Mustang Convertible?

I'm interested in buying a 1997 6 Cylinder Ford Mustang Convertible for $1500. The car runs very cleanly and it has like approx. 136,000 miles on it. The only problem is that it has been sitting in the sellers backyard for like 5 years. Could it sitting for that length of time have caused any major malfunctions that should prevent me from buying it?

Added (1). The seller has also said that the car has a new transmission if that helps any.

Yes. The transmission, differential, and engine are full of gunk by now. Liquids and lubricants will have dried out by now.

ANY vehicle that has been sitting out in the open, and unprotected from the weather is going to have some problems… The most serious problem would be RUST, especially in a convertible. Mustang convertibles use a fabric top which deteriorates fairly quickly and can develop leaks. These leaks allow water inside the interior, and THAT can rust out the floors and body structure.

Have the car inspected by someone who actually knows what they are looking for.

It's been sitting OUTSIDE for 5 YEARS… That is all you need to know to know this is a bad idea