What should i do about a sebaceous cyst that's been there years?

Observe vs Remove: Sebaceous cysts are benign and generally don't need to be removed unless they are bothersome or causing symptoms. There is a risk they can become infected. If this occurs, it would need drainage.

Remove or nothing: If it is small and not bothering you, leave it alone. These tend to enlarge because they are caused by skin surface cells trapped beneath the skin. These cells continually shed, increasing the size of the cyst (more accurately an epithelial inclusion cyst.) removal is generally a minor surgical procedure, but requires total removal of the cyst wall to prevent recurrence of the cyst.