Martin, good to hear of some progress.
One thing about the secondary, don't look at it in relation to the primary mirror. Only the focuser. Center the secondary to the inside edge of the Cheshire eyepiece. The Cheshire can be inserted quite deep into the OTA, and this is to facilitate the centering of the secondary to the inside edge of the Cheshire. Part of this process involves looking at the outside edge of the primary to see that it is co-centric to the edge of the secondary.
Once you have the secondary centred, you can begin tweaking its collimation screws to get the alignment of the center spot of the primary to the crosshairs of the Cheshire. Nothing else.
Once the crosshairs and center spot are aligned, then you can swap for the laser. You may find the laser is out from the center spot, but it should be bugger all. Once the laser is centered, you can then look at tweaking the primary's collimation.
One thing to look at is the secondary mirror's holder where the collimation screw push down onto the holder. The ends of these screws will be sharp, and because they are made of steel and the holder is soft aluminium, the screws most likely will have gouged the contacting surface of the holder. Also there will be a little play between the screws and the threads they are wound through. This play may mean that when you tweak the colli screws, the gouge marks may have the colli screws ease into these marks and in turn throw out your entire collimation process, and you will be cursing and screaming wondering what the hell is going on!!!!
Have a look at the secondary holder where the colli screws push against it. Check for gouge marks. If there are no matks, you are very lucky. If there are marks, there's some things that can be done to correct this. But first check the holder.
Alex.