Purely a personal opinion, but I try not to use oil flush on an engine unless I know it has had regular oil flushes and changes from new. Simply because imho if there is any chance of muck being present in the engine the last thing you want to do is to flush it all at once. If you use a flush and it loosens muck it may cause a blockage. I prefer to use frequent (5k) oil/filter changes which cleans the engine more gently.
I have used a flush on mine from new, oil/filter every 5k with a flush every 10k. Seems to work for me. It's done 94k and hasn't given a spot of bother.
I read somewhere that you can use oil for a diesel engine if you want an oil with higher detergent levels - but I can't vouch for that myself, just repeating what I've heard.
I use Mobil semi-synth 5W-30 in mine. And GM plugs. My 2001 Vectra has been the most reliable car I've ever had.