Stanwell, I would say 80% of the issues are quality control. It's one crisis to the next. Valves, rockers, collets, what is next? CASA are addressing this with them.
The other thing is the owners complying with the SB's.
When your LAME services your Cessna and you get $11,000 of sticker shock, you have no option but to pay it.
On the other hand, what is compelling you to upgrade the thru bolts on your owner maintained Jab? God, I've known of people that don't even have an engine or airframe log book! (Being careful with my words there)