It's definitely a crystal. The only identifying info I can find on mine is: "S3238E", which when I google brings up other threads including one you participated in over on AppleFritter. A thread over here indicates the SE/30 uses the same crystal, and according to schematics I've seen that crystal is 32.768 KHz. This is a very common frequency used for real-time clocks so it's no surprise that it's 32.768 KHz.

This will be a crystal you can find at any supplier. Just search for a through-hole 32.768 KHz crystal. You'll see plenty of results that look just like the original (cylindrical can, radial). The unfortunate thing is that I can't find anything about the original part number, so I don't know the details about the load capacitance of the crystal. Typically you're supposed to match the load capacitance to the circuit. You might just have to guess and hope it works (it will probably be fine).