The right tools and a little experience count for a lot, but geez, there's no subsititute for doing the job yourself when it comes to the details. On the other hand, I'm not sure it's really possible to do a car stereo install that can quickly disconnect back to pure stock condition.

If the car really has less than a year before you get rid of it, then just tighten everything up, maybe solder some of the wire-splices together and see what happens.

Otherwise, you might want to consider terminating both the sled harness and the BMW harness in some kind of quick-release crimpons and building your own adapters to sit in between. Basically replacing the orange RCA cables, and you'll probably need to create some kind of octopus ground lead with a single attachement to the car-side, but that can connect to all of the RCA grounds.

--Nathan