That dovetail is held in with a gib, which is why you have a gap. The chunk and cracks in THAT particular part may not be of any consequence. There isn't much load, and most operations do not require infeed on the tool's axis. Honestly, as the owner and user of such a grinder, I think that blemish is inconsequential to the sound operation of the tool. Now, for replacement parts, you're pretty much on your own to source or make the parts you need. Bearings require only a little bit of info to replace- ID, OD, and width. You can pick load rating and precision from what you find available in the sizes you need.