That might've happened to me. I just got a flat on the 300 the other day so I put on the spare. i'm gonna take it out to get it fixed today, so I'll see what the problem was. When i took it out I didnt see anything stuck in the tire(nails, etc.)..
If that's the case, how long would just having it cleaned and resealed last me? I've still got the stock rims, but probably going to fix up the sc in a few months, so probably new rims. I've got a 95 btw, and it needs a major tune up, but you know how much those cost.. <_<