eyebull,
I had exactly the same thing with my brand hew HW30S I bought late last year (laser etching on breech block, so relatively recent manufacture).
The piston seal was burnt, and also torn, and the spring was very bent (S-shaped).
I had put not one shot through the rifle, when I stripped it down, and found the below.
Did remedial work with the metal-work, put a PTFE block in the cocking arm, and fitted a Vortek PG2 kit.
Shoots sublimely now.
Have fun & a good Sunday
Best regards
Russ