First, I’d suggest using this technique to assess what type of finish is on your piece: https://www.wwgoa.com/video/what-finish-is-this-035160/
If you can’t identify it with confidence, you could strip or sand it off. If you want to try a less arduous approach first, scrub the piece with mineral spirits, apply a couple coats of this product https://amzn.to/3wxJwnf, then apply your new finish. That sealer has a good reputation for adhering to most finishes, so chances are it will stick to what is on there already, and allow you to add your preferred top coat over it.
Paul

Yes, epoxy would be fine. If it is a clean break, you could also probably use a regular PVA woodworking glue like Titebond.
Paul

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