Do the benefits of oil of sharpness stack with those of +1/2/3 magic ammunition?
I'm really just curious whether these also stack as +X ammo does with a +3 bow, or if there's a point at which things stop stacking.
According to the official rulings in the Sage Advice Compendium - page 18:
In general, bonuses stack, unless they’re from the same spell
Also, in the DMG - page 252:
When two or more game features have the same name, only the effects of one of them — the most potent one — apply while the durations of the effects overlap. [...] Game features include spells, class features, feats, racial traits, monster abilities, and magic items.
These are items but they do not have the same name so this rule does not apply.