Hi, Im new to this too.
i got a new spring and spring guide from Tinbum Tuning.

The difference is great, the rifle (HW35) no longer has that twang and wobble/vibration. It now just has a solid, precise thump. I was like you, thinking of polishing the inside of the piston cylinder but decided against it. I did polish the piston and debur the cocking guide.

A well fitted spring guide seems to be night and day.

New breech seal worked well too.

As others have said try to fiddle as little as possible to get a consistent rifle.