[abisel]

If you try to replace the tube yourself, be prepared for a lot of work.

You would need to fab up some kind of jig to hold the transmission mounts and the spring plate mounts in the proper orientation to the rest of the body.

You would need to grind through three weld beads on each end of the tube. One is outboard and obvious. A second is inboard and obvious. But the third is inside the quarter panel. The only way to get to this third weld would be to grind through the tube walls from inside the tube.

You would most likely have to cut a slit or two on the inboard side of one of the longitudinals just to get the replacement tube in place.

Also, you would most likely have to cut a couple access holes in the rear seat pan so that you can get a good weld all way round the tube in the inboard side of the longitudinal.

The shop manuals have a section on this type of repair.

If you have the tools and feel you can do the job, go for it. Otherwise, spend the extra money and have Porsche do it for you. Not something you would want to trust to someone without a jig. This area is critical to body/suspension alignment.