2004 Mazda RX8 carbon monoxide problem?

2004 Mazda RX8 is at a used car dealership for $5,000 in cash and it has around 50,000 miles. The problem with the car is that it has no A/C and there is a carbon monoxide stench in the car when it is on for a period of time. The previous owner has spent $8,000 on trying to find the solution to the carbon smell and couldn't find what the problem was. What could possibly be the problem? And is it a good deal if I buy this used car?