Sills Cross Section Diagram.

[ramjam2005]

Likewise, replacing a complete inner sill should be left to the professional workshops, as that's Major, Major surgery and risks the integrity and correct alignment of the whole body without a jig. Let alone the time and effort required to get at the thing. Repairing and re-fabricating the front 12" section was enough of a challenge for me and need to tackle the same on left hand side next !

[Goldstar]

I think I bought them expecting to chop them up if ever needed to repair - pretty thick gauge steel they used

[Philip Wardle]

I think I bought them expecting to chop them up if ever needed to repair - pretty thick gauge steel they used

Commencing in 2003 SOCTFL investigated the practicality of tooling for inner sills and/or repair panels for the bottom three or four inches where they rust, this work was done by Alan Bruce-Smith. The main cost drivers were the gauge of the metal as Paul has noted, and the depth of the channel where the wiring harness runs. These factors in turn meant that a larger than usual rubber press would have been required, of which there were (are?) only a few to which we might get access. The estimated cost of tooling was £18,000 (as of 15 years ago?).

Although the project wasn't taken forward at the time, SOCTFL invested £800 in taking flash moulds from an original pair of panels, which we were able to borrow, against the possibility that the project might go ahead in the future. Meantime, as others have said, restorers often prefer to repair the rusted areas rather than replace the whole thing.