Weatherproofing part-rotted hardwood threshold?

We have a large garden shed, it's a substantial timber framed thing and one end has a glazed door in the middle and glazed panels either side, all mounted on top of a hardwood threshold/step that's actually part of the structure. i.e. the whole end wall structure seems to have been built on top of this slab of wood and then put into place when the shed was built, so cutting it out from under isn't really an option.

The wood has rotted along part of its length. I've removed the soft material, applied wood hardener, and will put epoxy filler in to fill the hole, but I'd like to try and weatherproof to prevent further damage.

Would it be possible to use something like a lead flashing formed over the step?

Post a photo. A bit of lead would help, but are you sure there's no damp rising up from the ground?

Do you know what type of wood it is? And is it treated? Not all hardwood is rot proof.

Sorry will attempt to get a photo. Pretty sure there's no rising damp; the shed was in a poor state of repair for many years before we arrived and prior to replacing the roof (which I did last year) looks like water had been running down onto one particular part and once it had started to rot it's made a depression that the rain sat in and just got worse and worse over the years.

Not sure of the species of wood but it's been there a long while and the rest of it is sound. If I go the lead route (I've not worked with lead before) I'd plan to cut into the join between this section and the frames that sit on it, so I can tuck the lead under. What's the best way to fix the lead and fit it over the ends? (thanks for help and input btw)

Here's a photo of the offending article. Where it looks wet is just hardener going off.