I own a 40 year old shed with a steel roof that was fastened using gasketed nails. Over time the nails have worked loose and the gaskets disintegrated and many of the holes leak.
Will pulling them and replacing them in the same holes with screws designed for the job resolve the leaks, or at least most of them?
I would think that if the nails are the leak source then yes replace them with rubber gasket-ed screws, but put some quad sealant in each hole before driving the screw in.
If this roof in question is standing seam, then there shouldn't be any leaks because the fasteners are all concealed. Are you sure it isn't an exposed fastener roof? That's typically the type of roof that leaks when fasteners work their way out over time.
For exposed fastener roofs, they make gasketed "rescue screws" specifically designed to be fastened into the holes left behind by the old nails (or smaller screws). For example: http://stfasteningsystems.com/?page_id=467 (no affiliation). These should do the job just fine, provided that they hold. If the nail hole is very large, then the screws' holding power may be diminished.
If it's a standing seam roof, then I'm sure you can find some #14 pancake-headed screws that will serve the same purpose. The screws don't need to be gasketed, so just make sure the shank is larger than the old nail so it will hold properly.
