Scubapro MK25 bushing damage cause?

[Fibonacci]

Currently servicing two SP MK25 first stages, one near new the other seems to have had a hard life and not rinsed properly.
The spring had some surface rust which came off OK but the interface of the ground end of the spring to Bushing #10600135 had a deep groove worn into it!
I’m replacing it of course but just wondering if anyone could shed more light on why the plastic bushing should have such localised wear?
One clue may be due to it missing the piston stem o-ring #01050360 which caused the Bushing to move a bit lower and over compress one of the piston o-rings #01050177 but would that cause the deep scoring?

 

[happy-diver]

The previous dude butcherising it with sharp implements to clean off any previous rust
Look at different schematics and confuse yourself with the rubber bush there, no oring
Isn't the hole too big for an oring to have effect

 

[Fibonacci]

No the bushing is a very close fit to the piston shaft but not capable of fully sealing against HP air, the damaged reg missing the o-ring wouldn’t hold IP.
The newish one did have the o-ring fitted and IP locked up solidly.

 

[Mobulai]

I think the missing o-ring in the old schematic is because of the older piston (all metal not composite 2 part one) — I might be wrong tho

Could the spring have been twisting around anf digging in?

 

[Fibonacci]

The spring could have been twisting and scrubbing out under the ground area.
I just removed the spring in the pic, no cleaning yet.
You can see the metal in the ground area is relatively clean vs the rust on the spring surface.

 

[Tanks A Lot]

Is the spring still intact and true to it's original shape? What happens when you roll it on a flat surface, does it roll uniform or wobble around?
An out of shape spring will apply an uneven pressure to the mating surface, possibly resulting in what your picture shows.

As much as I love ScubaPro, the only times I ever had broken springs on first stages was on theirs.

The MK25 always had a composite piston as far as I'm aware. The O-ring was added in 2002 along with the washers and O-rings on the seat side.