Whats this bolt? + Shaft seals??

[ThotFeline]

help! What's this bolt? It's leaking oil and I know it's a silly question but can I remove it or is it holding something inside the engine, I cant see a clear reason for it to be there or for it to be leaking oil. its rear left of the engine going directly up just below the bottom of the sprocket cover. (see attachments)

I've also heard that you don't have to disassemble the engine to replace the output shaft and gear shifter seals, just pry them out carefully?

oil is defiantly coming from the output seal and the bolt mentioned but I'm replacing both shaft seals and the alternator cover gasket just to make sure its sorted.