Rusted, Loose Screws Metal Roof Attached to Metal Building

I have a 6,000 ft sq metal roof attached with screws to a metal roof truss system (metal beams, metal purlins) with closed cell spray foam insulation on the underside of the roof. After a heavy rain, I found a small leak dripping from a purlin onto my suspended acoustic tile ceiling. I went on the roof and a saw that the screws are rusted and in some places the previous owner (this was a firehouse owned by the town) had caulked around some of the screws. I found a screw that was loose and I could tighten with my fingers. I appears that some of the rubber washers have deteriorated. My inclination is to examine the screws and replace with new any that appear to have failed, possibly using a silicone caulk together with the new screws. I've read on this forum about using bigger screws but I think that refers to wooden rafters and I have steel substructure. What do you think? The roof itself is in good condition. Single long panels from the gable to the eave.

Thx for advice. Buying stainless steel screws from local vendor and will begin replacing worn out screws