Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
I always assumed that it was for harmonic dampening as it has no other apparent purpose. I can see how it might be for thermal insulation.the "bushing" is a wiper, and should go on above the plastic hood on the piston, riding on the piston shaft inside the spring. Again, IIRC, something for "icing"...
It seems pretty obvious that the extra plastic bits are for cold tolerance but was it done to make it more cold tolerant than the MK10 or just to offset the added cooling due to higher flow rate of the dull edge piston. If someone has the marketing info on the 10 plus it would be interesting to see what the selling points were. The only MK10 PLUS I ever got came with the centering washer broken so I converted it to MK10 and sold extra bits.Wasn't the original idea behind the 10+ for higher pressures (4k)? But then the thermal things (SPEC included as you will see most 10+ being SPEC) were "enhancements" for cold tolerance, including the "cap" on the piston?