Why would i want to collate stats on H2AD engine when i clearly would not touch another with a barge pole. In fact if i never saw one again or even heard one i would be happier. The original poster wanted advice and my advice remains to avoid this engine esp when D2j and E2D dont have the issues. Out of interest the history of this sad engine is interesting as it was introduced when Cessna were heading for trouble in the late 70's. I reckon they asked Lycoming for the cheapest 160 hp engine they could make - and they got what they deserved! No other engines require serious T bar mods and anti-scuffing additives so there is the admission.Cessna were bright enough not to stay with it long once they realised what deep joy "Blue Steel" brought. Please remember that if our pilot pilgrim here buys a dud it could put him off for a long time. In the USA and New Zealand(where i fly a bit) most folks have slung the H2AD and put a D2J in! Actually i can not remember seeing an H2AD ever down under - wonder why? To try to pretend there are no increased risks because you have been lucky with one or two units is to stand against the known facts.
Like a previous poster i no longer burn petrol in my 172's anyway as i am reluctantly having to get to grips with FADEC diesels - joy of joys.
Actually i think i should modify my advice to say just hire unless you are gonna fly a whole lot as owning and operating aircraft is altogether onerous at the Group A end!
Good luck whatever you do!
