[Bolin]

However, there is one disadvantage to them.....

In place, moisture sits between the pad and the body. Around the hole is a panel seam, between the main sill/car side and the internal jacking point support.

This seam has no seam sealer ans is only covered by paint. I have seen the paint over these seams crack at the point of the joint, presumably due to the small amount of flexing whilst jacking the car.

Potentially the moisture that sits between the pad and body could enter into the seam here to cause corrosion.

My solution was to apply flexible polyurethane sealant around the panel seam, which should prevent any problems. Alternatively a thin closed-cell foam gasket between the pad and body should work.

BUT - the main moisture ingress into the rear section of the sill appears to do far far more damage (i.e. corrosion) anyway, so these seams around the jacking points are probably not worth worrying about (unless you can prevent the main ingress).

I think the main moisture ingress route is via the final trim clip hole for the sill trim. The trim appears to move backwards a bit in use, seemingly causing the rear end of the trim to touch the sill and effectively pull the trim away from the body very slightly, which I think opens a small gap between the final trim clip and it's hole, allowing water to get in. I sealed the clips into place with polyurethane sealer/adhesive, so they are effectively glued, which should prevent the problem.

Of course I could be completely wrong on all this, but those were my conclusions from looking very carefully at both the cars I owned. The one I did the sealing to I have now sold so cannot report on the long-term effectiveness that this would have in preventing corrosion.