This is a well known problem with the E46 chassis. In fact that was once a recall from BMW on the matter, but that has now expired. What happens is flexing of the rear subframe and body eventually crack and in extreme cases, pull out, the driver’s side rear mount or the passenger side front mount from the body. BMW originally was replacing the entire body panel in this area. The problem with doing it this way is that it wasn’t a re-designed body panel, so the problem would just happen again. After that, they moved to injecting the area with expanding foam. This again doesn’t solve the problem, only slows it down.
The proper way to repair this situation and the only way that RRT will repair it, is to repair the initial damage so that the mounts are all back in the original position and then weld in a reinforcement kit. These additional steel plates not only seal in the first part of the repair, but make the entire area structurally stronger. This ensures that the problem will never happen again.
But RRT does not stop there. The interior void is cavity sprayed, then entire area is cleaned, primered, painted and undercoated. Additional steps like this is an example of why we have the reputation we do. Properly finishing the job ensures that the area does not rust and the interior panel do not corrode. The entire process takes between 2-3 days to complete.