Hi Andy,
Something I would add and I also found with mine is that over time screwing the secondary collimation screws in and out puts burrs on the secondary holder. This is not a major issue during normal collimation, however, when you remove the secondary and potentially the spider and you go to put it all back together again you may find ( as you have ) that you need to make rotational adjustments. When you try to align the secondary with your focuser it will line up but as you then tighten up the center screw the secondary will walk itself slightly back onto the previous grooves causing poor alignment. Luckily the solution to that is simple. Remove the secondary, remove the old burrs and fit a think fiber or nylon washer to the surface where the collimation screws make contact. Reassemble and problem solved. The other bonus of this is that you can rotate the secondary now while it has a slight tension on it as the washer creates a bit of a bearing surface. This maintains where you set it a lot easier than having it loose to move it.
I hope this helps
