I haven't had any problems with the reliability on the CD drives. The arcade environment is pretty tough on devices of this nature as it is, and that game is what, ten years old? The drive lasted this long. The drive I had to replace had clearly been dropped - it was in terrible condition. The drives are incredibly reliable in computers.
If I still had a board around here, I would be tempted to try replacing it with a hard disk to see if it would work. You can try it if you want, dd the CDROM disc image to a drive and hook it up with the same settings (ID, termination, etc) and see if it works. But... I almost think the CD drive is better for longevity, hard drives are fragile too, but if a hard drive breaks then you lose the data as well. At least with the CDROM, you need only switch out the drive - the disc will be fine.
-Ian