After dropping my shock off on Monday afternoon I had a call this morning to say it was ready ( 2 days later.)
The diagnosis was the main bush had all the PTFE worn off, down to the brass, which in turn made the oil black because it oxidises. There was very little gas pressure and the oil level was low. The main piston rod seal was still serviceable and the piston rod is still bright and not corroded.
It feels so much better now, definitely won't be a problem for next month's MOT
DM are an 'old school' type place with a healthy motorcross side to the business from the looks of it. They had shocks on the bench from Orkney, Shetland and other far off places , all for rebuilding, their reputation is excellent
Cost to strip, replace the bush, clean, refill and regas it.... £86 (the bush was £6 of that)
The only problem can come if the piston rod oil seal fails, because they're not a part you can order.....in which case I'm assured they'll rework the bottom cap to take a heavy duty motorcross seal.
They keep chrome rod in stock for making new piston rods, and regularly work on 1950's and 1960's off road bikes as well as modern stuff