Some light at last....
Say I pay your £5.3k figure to "buy" 1/4 of the engine fund on top of the value of the aircraft and the engine goes tits up I have paid for 1 quarter of the aircraft and I have paid £300 towards someone else's flying and I still have to pay 1/4 of the repair bill.
Better idea...... I pay 1/4 the value of the aircraft. The engine goes bang, the group uses the money in the bank to pay the repair bill and I am liable for 1/4 of the balance after that money has been spent. So the money in the bank covers the wear and tear that has already occurred which is why it was collected in the first place and I cover my % of the bill.
This is obviously where we are looking differently at things.
I don't understand why you would think you'd have to pay a full 1/4 of the repair bill? I can't see anything happening in such a senario other than what you suggest is a better idea in the second paragraph. The engine fund pays for the repair bill so far as is possible, and then the balance is split four ways. After all that's the whole point in having an engine fund.
If you don't see it being used for the repair of the engine, how do you see it being used?
dp