I go off roading in jeeps a lot, and our group is all guys with fairly well set-up vehicles, all of them reliable. When a new guy comes out that's fine, but their junk better hold together. If they break we'll get you out, but that's it. Next time that person is not invited unless they have made noticeable changes to their rig, and seem ready to go.
I've personally told friends they can't come, and feel like an ass doing it. But, when you spend your whole weekend fixing someone else's junk you end up ruining yours. We went out once last spring, and I went with a few friends friday and saturday, then met up with the actual guys I ride with on sunday. I spent all of friday and saturday running parts back and forth, because my truck is the only one that was holding together. Sunday I told those guys not to come out, and I went off with the group I normally ride with. Felt bad, but that's how it is sometimes.
When I first started riding with those guys my CJ was a 'chronic breaker' with dumb stuff always going wrong. It didn't take long before I quit going out, built a Ford Ranger right, and went back to riding with them.