I;ve been working at my local bike coop as a head mechanic for a couple hours each week. A couple weeks ago at the bike coop, a guy brought in his old Cannondale MTB that he's been using and abusing as a beater commuter for years. The rear wheel keeps popping out of the dropouts, and at first I thought it was because the rear wheel bearings were pretty much seizes, so we gave him a used wheel and sent him on his way.
Last night he came back, and said it works much better now, but the wheel is still popping out on steep hills. So I put the rear wheel in real tight, put it in the lowest gear with the front wheel against the wall, stepped on a pedal and proceeded to watch the frame flex like a noodle as the rear wheel popped out. Inspecting the frame I discovered a hole in the non drive side chainstay right where it's welded to the Bottom bracket, and both vertical dropouts have the front edge ground down from the wheel sliding forward so many times. He said that hole has been there as long as he's had that bike.
My diagnosis was "This frame is shot you shouldn't ride it any more", but I was also on my way out, and the next head mechanic was taking over, so I asked his opinion. Then he started trying to jerry rig an old Derailer hanger to capture the axle on the drive side so it couldn't pull forward. Now this plan might work to keep the axle from pulling out, but even if it does I don't feel comfortable suggesting there is anything that can be done to make this frame rideable again.
The primary purpose of the bike coop is to help people make sure their bikes are safe, and to help make biking affordable to all. I tried to make it clear I didn't feel that frame was safe, but other mechanics were more concerned with trying to make it work for this guy. I would have rather move his parts to another frame. He felt like he didn't want a "downgrade" now this once was a nice frame, but with all that flex, and the wheel popping out, and the potential for catastrophic failure, I feel like a gaspipe huffy would be an upgrade.
I tried to make it clear I felt that this bike was due unsafe, and that solving the wheel slipping problem would only serve to put a bandaid on a broken bone. But everyone else seemed determined to make it work for him. Now the guy is a hammerhead who apparently thinks nothing of pounding around on seized up wheelbearings, I'm thinking that the wheel slipping was just another sign of failure that he's choosing to ignore. He'll keep riding that thing until he can't. He'll ride that frame until it breaks, and I wouldn't dream of trying to stop him, but ethically I think it's wrong to help him do it.
I realize no professional shop would have touched that with a ten foot pole, but bike coops have a sort of a make-do attitude, which I think is great up to a point. We fix a lot of bikes for $15 or $20 worth of used parts that the bike shop would turn away, because the cost of new parts was prhibitive. In the end I guess I did the best I could in trying to explain why an aluminum frame in that kind of condition was not worth jerry rigging, but how would you have handled it.