Well, dismantled the forks as far as needed removed the springs and checked the oil levels in both forks. One was way, way over where it should have been the other was way down on what it should have been.
So I sorted the level in both forks and re-assembled with the same springs, not the heavier weight ones as planned initially ( difficult, I don't have them yet)!.
Marzocchi suggest max 15mm of sag I can get about to about 18mm with 10 turns of the preload dial but the forks now feel beautifully plush and smooth. Loads more preload there if needed but i did read somewhere to try and keep that to a minim for better overall performance and spring life, so I'll see how it goes.
I have not had chance to get out on the bike yet as I have only just put everything back together but the difference in what they feel like now and when they came back from the shop after their second attempt to get them right is worlds apart.
Will let you know how I get on after the first ride.
Very simple process if you follow the manual and are logical in your approach.
Thanks for help everybody