$12,000 annual?
I find it difficult to comprehend that an annual inspection on a C150 would cost GBP 8000 unless someone is getting really, really screwed, big time.
We've had a fleet of as many as 15 of these things (and a few 152s), some of which have been around since 1991, and have been enthusiastically and regularly abused by legions of student pilots - and we have not seen anything like "major airfarme parts wearing out". Someone is getting hosed . . .
I'm also a technical advisor to the Cessna 150/152 club (since 1982), and if this was an ongoing problem, I would have heard of it by now from more than a few of our several thousand members worldwide.
The Cessna 150/152 is one of the most rugged, durable and trouble free aircraft you can buy. No, it isn't fast, no it isn't sexy, but it will NOT eat you out of house and home - parts are widely available, and if you shop around at all, quite reasonable, even by aircraft standards.
The airframe parts that "wear out" are as follows - the seat pans crack in high hour trainers from all the people jumping in and out of them. These can be patched. The flap tracks sometimes wear, this is a fiddly repair, but not hugely expensive. Sometimes you will find corrosion on the inside of the flap well, get out the drill and rivet gun and a bucking bar. Firewalls and engine mounts take a beating in rough landings, but that is accident damage, not "wearing out". Finally, every once in a while you might see corrosion on the main spar cap. Again, not a trivial job, but nowhere near $12,000 (much closer to $2,000, and that's at retail).
For $12,000, I'd expect most of a restoration, this much for an annual inspection is downright criminal. For $12,000 I could make a garden-variety Cessna 150 or 152 fly like a new airplane. For $24,000, you'd also get a zero time engine, new windows, new paint, upholstery, and other stuff. For $36,000, you'd have a Garmin 430 in it as well.
I'd be VERY interested in seeing the actual repair order which resulted in this bill, not once, but what, two years running? Or was it three? I think this tale has grown in the telling.
Best Regards,
Echo Mike