If you are careful and do not mess with the ring and dislocate it, you do not need to worry.

The Varnish...

Forget it alltoghether.

If you said thick coal deposits in exhaust port and piston top, but varnish...

If you mess with your engine and remove the normal internal patina, you will just harm it.

You should not try to repair something that is not broken.

I know it is fun to dissassemble engines and loo at the cute connecting rods and pistons.

But frankly, unless your engine does not work, you should not dissassemble it.

Cheers,
Ikaros