That machine is not a PCI Mac, it is a NuBus one. Physically, the board is the same as the 6400, but it isn't as well designed. The 6300's board is basically a 6200's board with a 100/120Mhz 603e. Because of this similariaty, they're usually thought of as one of the worst Macs ever made. Their 4.5 volt batteries are not prone to leaking expect in extreme cases as Rayovac designed the battery casings very well. I'd be more worried about the possible inclusion of the Apple remote's two AA batteries. But not all 6300's came with an Apple remote, most didn't. The capacitors on mid 1990's boards are still good and have about 5 years left in them. They're more robust that the 1980's boards as not as failure prone and the bad batch ones made in the early half of the 2000's. I suggest leaving it sealed.