My Mk6 bought from new, never touched in-between and was refurbed by me four years ago came a nylon head which had no scraper ring. I replaced it with an aly version from John Knibbs. T20 is right the later loading taps leak like sieves.
When I can get my act together and work out what else is wrong I'll do an update on my attempt to have groves machined and fit orings either side of the tap.
It was seized up. I used a screwdriver and hammer to push the piston down the cylinder after trying to squirt WD 40 every where to loosen it. Shades of the Meteor thread.
Perhaps some one should market the buffer washer material as a bonding agent.