I was thinking the same about the flush, just wanted to see what other people thought. In regards to the underside of the rocker cover, mine has just 2 holes, 1 for the PCV valve and the other is a breather, cant get my finger under there cause there is a plate to stop oil flying up into the breather.

With the oil, I've already gone and bought Edge 25W-50 and hope to change it this weekend. As for winter in North QLD, the coldest we would get would be 12-14 degrees, and only for a few days. Rest of the time is bloody hot. As your have already read, the previous owner was using Course Plus - a 25W-60, too thick IMO.
Will let you know how it goes after the change.