Find an independent service "bloke" and let him/her do it. Only an hours labour and it will be spot on.

These are my go to guys

https://www.lsengineers.co.uk/stihl-petrol-chainsaw-ms-parts/stihl-ms170-spare-parts.html

Stick with genuine Stihl parts, pattern stuff is pretty poor. You’ll find plenty of clips on YouTube on repairs. The Chainsaw Guy in Myrtle Creek, Oregon has the best no nonsense advice

As above, only use Stihl spares.

Nothing is that hard you can't do it yourself but a wee service won't break the bank if you get a dealer to do it.

Another vote for LS.
Yes, if there’s a groove in the sprocket it needs changing. They aren’t that expensive or indeed hard to do, just watch out for the circlip pinging off onto the aether....

Maybe change to a rim sprocket

Have you run it without the bar to check that the oiler pump has gone?
It may be that the hole in the bar is blocked.

Yes it's agree that's most likely. Can often unblock it with a good blow down the hole.

Can often unblock it with a good blow down the hole.

I once knew a girl like... Errrm, never mind. As you were 🙃

I prefer the oregon brand instead of the stihl brand.

Do you ?. Handy to know lol.

As above, only use original Stihl spares.