[swifty]

In that case Garyh i found it easier if the piston was pushed as far into the caliper as is possible, the rubber dust seal sits in the piston groove and also rest down onto the caliper body if that makes sense.

The retaining dust seal ring can then be eased over the rubber to grip the caliper body, i maybe should of taken a few photos as it easier to explain with pictures than it is with words, as they say a picture speaks a thousand words.

One more thing you mentioned splitting the caliper body, if you do make sure you retain the small black rubber seal that sites between the two halfs where the brake fluid passes, you don't get a new seal in the caliper repair kit.