been having a good nose around under my car for last few days. as under the engine was a bit of a mess. theres is no rot on the underside of my saff that i am happy to report

however, it has been jacked up and various points in its life, and this seems to have taken the underseal off in certain places. i wanna wire brush the old stuff and reapply to prevent any more rusting in future.

as i have never undersealed a car before, what the procedure, not doing the whole car, just spots, but looking to find what the HARDEST WEARING underseal is to put on these areas.

it has been jacked up from four different spots at the front (2 each side) and 1 each side at the back.

any advice please guys