If you don't see it being used for the repair of the engine, how do you see it being used?
This is another valid angle. Sometimes, the engine fund isn't used towards a new/overhauled engine. The group might get disbanded (let's say the plane gets wrecked and the insurer won't cover it, or is scrapped because some huge problem is found which would cost too much to fix. Then, the fund might get used towards buying another plane.
In the group accounts, one would normally work things on a going concern basis i.e. you assume that the "business" will continue, and you make a provision for the anticipated engine work by building up the fund. But the fund isn't held in any kind of escrow and can be used for anything at all. In an extreme case, the group might get disbanded altogether in which case the current members will pocket the fund!
There is NO way to work this with perfect fairness, in any group that has some member rotation. Somebody will benefit from the others, depending on luck, or inside knowledge.
It's a bit like the treatment of fuel duty drawback within groups. Many groups, to my amazement, allow the pilot going abroad to pocket the drawback. This pilot is then screwing those who might fly it abroad (still on the same fuel load) later; they can't make the drawback. When I used to rent my plane out, I didn't have any rules set on this and one renter (an instructor, no less) pocketed the drawback of about £100 which completely covered the cost of his trip to LeTouquet and back... another instructor/renter pocketed a drawback without even telling me and it was by accident that I avoided making a duplicate claim.
I think a lot of the arguments in this thread come from the lack of appreciation that there is no perfect way to run these maintenance funds, in any group that has any member rotation. Only if all members remained for the entire period the plane is in the group could one work it out fairly to all.