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.