Hello - I am new to the Crossfire world and I know that our Crossfires did not come with a spare or even a donut spare. I would like to have a donut. I have read some other threads on this forum and its seems like a SL500 donut will fit on a Crossfire Coupe. But, it also seems like the SLK320 came with a spare - is there any reason why that would not work on a Crossfire Coupe?? Thanks.