The sills on my zed are actually pretty good. There were one or two small holes which I've treated and patched up and have had a good dig at the rest of them with a screw driver to make sure it's all solid. I was going to drill a couple of holes and attempt to treat the insides so that they don't give me trouble in the future. I've heard the inner sills are multi layer. Can anyone advise how best to go about doing the job?

Some members here have treated there inner sils with protective oils and there should be threads about it. The best way is not to drive your z on salted roads and always wash the inner arches of any build up of dirt.

No need to drill holes:

 

When you are using cavity wax in the sill sections (I used Dinitrol aerosol cavity wax with 60cm lance) it helps to know

where you are trying to get to with the product. This photo shows the complex sill structure in cross section. You can get

at the various sections from inside the car, the plastic door sill plate fixings and the hole at the front of the sill located

behind each front plastic wheel arch liner.

 

 

Full thread here: http://www.300zx.co.uk/forums/showthread.php?180582-How-much-rust-is-too-much&p=1862625&viewfull=1#post1862625

Unfortunately avoiding salted roads might be difficult as it's going to be my daily driver! I will keep an eye on the inner arches though.

Thanks Andrew, that information is massively helpful, glad I won't have to drill them at all. Will have my fingers crossed when I remove the liners!!