I had a couple of related issues with my DSV, sometimes leaking other times after sitting in my dive bag, over time the o-rings would lock it up almost solid.
Even in the water operation would be very stiff and tend to rotate the entire assembly in the hose a bit meaning the DSV mouthpiece was not oriented in the most comfortable position. Tried multiple different types of o-ring lube, no difference.
Located in Australia, service kits are a long way off and shipping is expensive.
So... I decided to experiment with different Duro o-rings after a chance comment by Peter Katz (of Sea Hornet regulator fame) who said they had a lot of trouble with the rotating Turbo Boost collar o-ring tension causing it to become unusably stiff in storage/transit to the customer. They changed o-ring spec from 70 Shore A to 50 Shore A and had no further problems.
I ordered in some 50-70-90 Shore A o-rings to test:
ASA568-028 for the inner barrel and mouthpiece port, -027 for the wagon wheels.
90 SA worked for a time then locked up solid, worse than OEM condition.
70 SA seemed to perform same as OEM
50 SA worked very well, deformed easily so no more lockups or leakage!
Only issue being so soft they were sensitive to being cut a little by the mouthpiece aperture if you are not careful to rotate the barrel during installation.
BUT it has reliably fixed the issue...
Regarding the annular scratches in the bore , my DSV was like that from new... appears to be post-moulding CNC machining marks to remove draft and introduce the undercut around the inside of the mouthpiece aperture.
Smoothing with some 600-800-1200 grit wet and dry paper might help but all my issues were resolved with just changing to 50 Duro o-rings.
'A man can never have too much red wine, too many books or too much ammunition' Rudyard Kipling