“Is there any way to protect yourself from this? I'm thinking of buying a share, but don't want to buy in and a week later the engine to go bang and get a £15,000 bill which I have to fork out 25% of..... “
Avoiding this is not that hard.
1 Find a tame engineer who is knowledgeable on type and who you know. Arrange to take him over to do an inspection. Pay cash and it will not be too expensive.
2 Talk to the other members. I am a penniless enthusiast so this bit is easy for me. Let them know who you are etc but make it clear you are short of cash and will not be able to afford any big bill if it comes too soon after the share purchase. If the group still want you, you are dead safe! I have even had groups who have an easy payment plan if one member gets into financial trouble.
3 Talk to the engineer who is looking after the aircraft. If he says the plane if fine, he will look very silly if it falls apart. I find most will give you a honest answer because otherwise you will push to move the maintenance else ware and word of this will spread and he will lose business.
4 Take to the non-shareholders who fly regularly at the club and know the aircraft and the group. If the thing is about to break and anybody knows about it, they will have got the rumour. Your engineer will then have a good look in the right place.
Lastly, I have to add that I have been in and around group owned aircraft for many years and I have never come across this actually happening.
Rod1